Per-environment string identifiers like ``mujoco:tendon_label`` were
keeping their source proto path after replication, because
``_rename_builder_labels`` only walked built-in label arrays
(body/joint/shape/articulation). Tendon names therefore showed
``env_0/...`` for every environment, even though the tendon counts
themselves were correct.

Generalize the rewrite to also walk any string-typed custom-attribute
column whose frequency declares a sibling ``references="world"``
companion. This is the same data shape the solver already uses to
declare per-world parameter columns, so any future solver-registered
string column is handled without changes here. The existing
``startswith(src_path)`` guard makes the rewrite a no-op for non-path
strings, leaving them untouched. ``constraint_mimic`` joins the
built-in pass for completeness.

Also add a TODO on ``_scope_custom_frequencies`` pointing at
newton-physics/newton#2659 (commit 1d22547). Once the IsaacLab Newton
pin includes that commit, ``parse_usd`` scopes the walk to
``root_path`` itself and the wrapper becomes a redundant identity
check on already-in-scope prims; the shim can then be removed.

Per-environment string identifiers like ``mujoco:tendon_label`` were
keeping their source proto path after replication, because
``_rename_builder_labels`` only walked built-in label arrays
(body/joint/shape/articulation). Tendon names therefore showed
``env_0/...`` for every environment, even though the tendon counts
themselves were correct.

Generalize the rewrite to also walk any string-typed custom-attribute
column whose frequency declares a sibling ``references="world"``
companion. This is the same data shape the solver already uses to
declare per-world parameter columns, so any future solver-registered
string column is handled without changes here. The existing
``startswith(src_path)`` guard makes the rewrite a no-op for non-path
strings, leaving them untouched. ``constraint_mimic`` joins the
built-in pass for completeness.

Also add a TODO on ``_scope_custom_frequencies`` pointing at
newton-physics/newton#2659 (commit 1d22547). Once the IsaacLab Newton
pin includes that commit, ``parse_usd`` scopes the walk to
``root_path`` itself and the wrapper becomes a redundant identity
check on already-in-scope prims; the shim can then be removed.

The Newton 1.2 release includes the upstream tendon-scoping fix
(newton-physics/newton#2659), which scopes ``parse_usd``'s custom-
frequency walk to ``root_path`` natively. Bumping the Newton pin
removes the cross-source ``MjcTendon`` contamination IsaacLab
previously had to work around at the framework layer.

Pin bumps:

* ``source/isaaclab/setup.py``: ``warp-lang==1.12.0`` →
  ``>=1.13.0``, ``mujoco==3.6.0`` → ``==3.8.0``,
  ``mujoco-warp==3.6.0`` → ``==3.8.0.1``.
* ``source/isaaclab_newton/setup.py``: same mujoco / mujoco-warp
  bumps; Newton pin → ``v1.2.0rc1``.
* ``source/isaaclab_visualizers/setup.py``: 3 × Newton pin →
  ``v1.2.0rc1``.

Code adapts:

* ``source/isaaclab_newton/isaaclab_newton/physics/newton_manager.py``
  and ``source/isaaclab_ov/isaaclab_ov/renderers/ovrtx_renderer_kernels.py``:
  ``wp.math.transform_to_matrix`` → ``wp.transform_to_matrix``. The
  ``wp.math`` namespace was removed in ``warp-lang`` 1.13.

Per-env label rename:

* ``_rename_builder_labels`` now walks string-typed custom-attribute
  columns whose frequency declares a ``references="world"``
  companion (e.g. ``mujoco:tendon_label``), rewriting the per-row
  source-path prefix to the destination world root. ``constraint_mimic``
  joins the built-in label pass. The prefix match uses a path-separator
  boundary so source paths that share a string prefix
  (``/Sources/protoA`` vs ``/Sources/protoAB``) do not cross-
  contaminate. Newton's ``add_builder`` copies labels verbatim and
  tracks env identity in ``*_world`` int columns; the IL rename is
  the structural translation between Newton's labeling model and
  IL's per-env USD-path model. Both passes (built-in label arrays
  and string custom-attribute columns) remain necessary after the
  Newton bump.

Adds ``test_rename_builder_labels.py`` with 10 cases covering the
two passes, multi-source prefix-overlap regression, sparse env ids,
multi-frequency, multiple string columns at one frequency, and
empty-values pass-through.

The Newton 1.2 release includes the upstream tendon-scoping fix
(newton-physics/newton#2659), which scopes ``parse_usd``'s custom-
frequency walk to ``root_path`` natively. Bumping the Newton pin
removes the cross-source ``MjcTendon`` contamination IsaacLab
previously had to work around at the framework layer.

Pin bumps:

* ``source/isaaclab/setup.py``: ``warp-lang==1.12.0`` →
  ``>=1.13.0``, ``mujoco==3.6.0`` → ``==3.8.0``,
  ``mujoco-warp==3.6.0`` → ``==3.8.0.1``.
* ``source/isaaclab_newton/setup.py``: same mujoco / mujoco-warp
  bumps; Newton pin → ``v1.2.0rc1``.
* ``source/isaaclab_visualizers/setup.py``: 3 × Newton pin →
  ``v1.2.0rc1``.

Code adapts:

* ``source/isaaclab_newton/isaaclab_newton/physics/newton_manager.py``
  and ``source/isaaclab_ov/isaaclab_ov/renderers/ovrtx_renderer_kernels.py``:
  ``wp.math.transform_to_matrix`` → ``wp.transform_to_matrix``. The
  ``wp.math`` namespace was removed in ``warp-lang`` 1.13.

Per-env label rename:

* ``_rename_builder_labels`` now walks string-typed custom-attribute
  columns whose frequency declares a ``references="world"``
  companion (e.g. ``mujoco:tendon_label``), rewriting the per-row
  source-path prefix to the destination world root. ``constraint_mimic``
  joins the built-in label pass. The prefix match uses a path-separator
  boundary so source paths that share a string prefix
  (``/Sources/protoA`` vs ``/Sources/protoAB``) do not cross-
  contaminate. Newton's ``add_builder`` copies labels verbatim and
  tracks env identity in ``*_world`` int columns; the IL rename is
  the structural translation between Newton's labeling model and
  IL's per-env USD-path model. Both passes (built-in label arrays
  and string custom-attribute columns) remain necessary after the
  Newton bump.

Adds ``test_rename_builder_labels.py`` with 10 cases covering the
two passes, multi-source prefix-overlap regression, sparse env ids,
multi-frequency, multiple string columns at one frequency, and
empty-values pass-through.

The Newton 1.2 release includes the upstream tendon-scoping fix
(newton-physics/newton#2659), which scopes ``parse_usd``'s custom-
frequency walk to ``root_path`` natively. Bumping the Newton pin
removes the cross-source ``MjcTendon`` contamination IsaacLab
previously had to work around at the framework layer.

Pin bumps:

* ``source/isaaclab/setup.py``: ``warp-lang==1.12.0`` →
  ``>=1.13.0``, ``mujoco==3.6.0`` → ``==3.8.0``,
  ``mujoco-warp==3.6.0`` → ``==3.8.0.1``.
* ``source/isaaclab_newton/setup.py``: same mujoco / mujoco-warp
  bumps; Newton pin → ``v1.2.0rc1``.
* ``source/isaaclab_visualizers/setup.py``: 3 × Newton pin →
  ``v1.2.0rc1``.

Code adapts:

* ``source/isaaclab_newton/isaaclab_newton/physics/newton_manager.py``
  and ``source/isaaclab_ov/isaaclab_ov/renderers/ovrtx_renderer_kernels.py``:
  ``wp.math.transform_to_matrix`` → ``wp.transform_to_matrix``. The
  ``wp.math`` namespace was removed in ``warp-lang`` 1.13.

Per-env label rename:

* ``_rename_builder_labels`` now walks string-typed custom-attribute
  columns whose frequency declares a ``references="world"``
  companion (e.g. ``mujoco:tendon_label``), rewriting the per-row
  source-path prefix to the destination world root. ``constraint_mimic``
  joins the built-in label pass. The prefix match uses a path-separator
  boundary so source paths that share a string prefix
  (``/Sources/protoA`` vs ``/Sources/protoAB``) do not cross-
  contaminate. Newton's ``add_builder`` copies labels verbatim and
  tracks env identity in ``*_world`` int columns; the IL rename is
  the structural translation between Newton's labeling model and
  IL's per-env USD-path model. Both passes (built-in label arrays
  and string custom-attribute columns) remain necessary after the
  Newton bump.

Adds ``test_rename_builder_labels.py`` with 10 cases covering the
two passes, multi-source prefix-overlap regression, sparse env ids,
multi-frequency, multiple string columns at one frequency, and
empty-values pass-through.

The Newton 1.2 release includes the upstream tendon-scoping fix
(newton-physics/newton#2659), which scopes ``parse_usd``'s custom-
frequency walk to ``root_path`` natively. Bumping the Newton pin
removes the cross-source ``MjcTendon`` contamination IsaacLab
previously had to work around at the framework layer.

Pin bumps:

* ``source/isaaclab/setup.py``: ``warp-lang==1.12.0`` →
  ``>=1.13.0``, ``mujoco==3.6.0`` → ``==3.8.0``,
  ``mujoco-warp==3.6.0`` → ``==3.8.0.1``.
* ``source/isaaclab_newton/setup.py``: same mujoco / mujoco-warp
  bumps; Newton pin → ``v1.2.0rc1``.
* ``source/isaaclab_visualizers/setup.py``: 3 × Newton pin →
  ``v1.2.0rc1``.

Code adapts:

* ``source/isaaclab_newton/isaaclab_newton/physics/newton_manager.py``
  and ``source/isaaclab_ov/isaaclab_ov/renderers/ovrtx_renderer_kernels.py``:
  ``wp.math.transform_to_matrix`` → ``wp.transform_to_matrix``. The
  ``wp.math`` namespace was removed in ``warp-lang`` 1.13.

Per-env label rename:

* ``_rename_builder_labels`` now walks string-typed custom-attribute
  columns whose frequency declares a ``references="world"``
  companion (e.g. ``mujoco:tendon_label``), rewriting the per-row
  source-path prefix to the destination world root. ``constraint_mimic``
  joins the built-in label pass. The prefix match uses a path-separator
  boundary so source paths that share a string prefix
  (``/Sources/protoA`` vs ``/Sources/protoAB``) do not cross-
  contaminate. Newton's ``add_builder`` copies labels verbatim and
  tracks env identity in ``*_world`` int columns; the IL rename is
  the structural translation between Newton's labeling model and
  IL's per-env USD-path model. Both passes (built-in label arrays
  and string custom-attribute columns) remain necessary after the
  Newton bump.

Adds ``test_rename_builder_labels.py`` with 10 cases covering the
two passes, multi-source prefix-overlap regression, sparse env ids,
multi-frequency, multiple string columns at one frequency, and
empty-values pass-through.

After Newton's add_builder copies proto rows into the merged builder
for each environment, every row's label still references the source
proto path. Newton tracks env identity in *_world int companion
columns; IsaacLab keys data flow off USD prim paths, so each row's
label needs to be rewritten to its per-env destination path.

_rename_builder_labels now walks two kinds of label-bearing columns:

* Built-in label arrays (body, joint, shape, articulation,
  constraint_mimic, equality_constraint), each paired with its
  matching *_world int column.
* String-typed custom-attribute columns (e.g. mujoco:tendon_label)
  paired with a references="world" companion at the same frequency.
  Any future solver-registered string column at a frequency that has
  a references="world" companion is handled automatically.

The prefix match uses a path-separator boundary
(``src_path.rstrip("/") + "/"``) so a source path that is a string
prefix of another (``/Sources/protoA`` vs ``/Sources/protoAB``) does
not cross-contaminate when both feed the same envs.

The function raises ValueError if the parallel arrays of labels and
worlds have mismatched lengths, instead of silently truncating.

Adds test_rename_builder_labels.py with 10 cases covering both
passes, multi-source prefix-overlap regression, sparse env ids,
multi-frequency, multiple string columns at one frequency, and
empty-values pass-through.

Stacks on top of isaac-sim#5523 (Newton v1.2.0rc2 bump). The Newton 1.2
release also includes upstream newton-physics/newton#2659 which
scopes parse_usd's custom-frequency walk natively, removing the
cross-source MjcTendon contamination IsaacLab previously had to
work around at the framework layer.

After Newton's add_builder copies proto rows into the merged builder
for each environment, every row's label still references the source
proto path. Newton tracks env identity in *_world int companion
columns; IsaacLab keys data flow off USD prim paths, so each row's
label needs to be rewritten to its per-env destination path.

_rename_builder_labels now walks two kinds of label-bearing columns:

* Built-in label arrays (body, joint, shape, articulation,
  constraint_mimic, equality_constraint), each paired with its
  matching *_world int column.
* String-typed custom-attribute columns (e.g. mujoco:tendon_label)
  paired with a references="world" companion at the same frequency.
  Any future solver-registered string column at a frequency that has
  a references="world" companion is handled automatically.

The prefix match uses a path-separator boundary
(src_path.rstrip("/") + "/") so a source path that is a string
prefix of another (/Sources/protoA vs /Sources/protoAB) does not
cross-contaminate when both feed the same envs.

The function raises ValueError if the parallel arrays of labels and
worlds have mismatched lengths, instead of silently truncating.

Adds test_rename_builder_labels.py with 10 cases covering both
passes, multi-source prefix-overlap regression, sparse env ids,
multi-frequency, multiple string columns at one frequency, and
empty-values pass-through.

Stacks on top of isaac-sim#5523 (Newton v1.2.0rc2 bump). The Newton 1.2
release also includes upstream newton-physics/newton#2659 which
scopes parse_usd's custom-frequency walk natively, removing the
cross-source MjcTendon contamination IsaacLab previously had to
work around at the framework layer.

## Summary

Bumps the Newton pin to
[`v1.2.0rc2`](https://pypi.org/project/newton/1.2.0rc2/), which pulls in
IsaacLab-relevant fixes plus the upstream tendon-scoping fix.

## What's new in Newton v1.2.0rc2 vs IsaacLab's current pin (`a27277e`)

The current IsaacLab Newton pin is from late April; v1.2.0rc2 is the
latest release-candidate cut. Notable fixes pulled in:

-
**[newton-physics/newton#2659](newton-physics/newton#2659
\"Scope USD custom-frequency parsing\" — `parse_usd` now scopes the
custom-frequency walk to `root_path` natively.
-
**[newton-physics/newton#2678](newton-physics/newton#2678
Regression fix.
-
**[newton-physics/newton#2720](newton-physics/newton#2720
`SolverKamino` reset under `world_mask`.
-
**[newton-physics/newton#2710](newton-physics/newton#2710
VRAM leak fix on example reset.
- Plus 16 other smaller fixes between rc1 and rc2.

## Required dep bumps

Newton 1.2.0rc2's \`pyproject.toml\` requires:

- \`warp-lang==1.13.0\`
- \`mujoco==3.8.0\` (was 3.6.0)
- \`mujoco-warp==3.8.0.1\` (was 3.6.0)

Pins updated in:

| File | Change |
|---|---|
| \`source/isaaclab/setup.py\` | \`warp-lang==1.12.0\` → \`==1.13.0\`;
\`mujoco==3.6.0\` → \`==3.8.0\`; \`mujoco-warp==3.6.0\` → \`==3.8.0.1\`
|
| \`source/isaaclab_newton/setup.py\` | mujoco / mujoco-warp bumps;
Newton pin → \`v1.2.0rc2\` |
| \`source/isaaclab_visualizers/setup.py\` | 3× Newton pin →
\`v1.2.0rc2\` |
| \`tools/wheel_builder/res/python_packages.toml\` | All four pins
mirrored |

## Code adapts

\`warp-lang\` 1.13 removed the \`wp.math\` namespace. Two IsaacLab call
sites use it:

-
\`source/isaaclab_newton/isaaclab_newton/physics/newton_manager.py:72\`
-
\`source/isaaclab_ov/isaaclab_ov/renderers/ovrtx_renderer_kernels.py:330\`

Both rewritten as \`wp.math.transform_to_matrix(...)\` →
\`wp.transform_to_matrix(...)\`. That's the only IsaacLab-side adapt
needed.

## Test plan

- [x] \`./isaaclab.sh -i newton\` clean install against the bumped pins.
- [x] \`pip list\` confirms \`newton 1.2.0rc2\`, \`warp-lang 1.13.0\`,
\`mujoco 3.8.0\`, \`mujoco-warp 3.8.0.1\`.
- [x] Sanity smoke: Shadow-Hand-Over MAPPO (4 envs, 1 iter) runs clean —
simulation init through CUDA graph capture through one training step +
checkpoint save, no errors.
- [x] Pre-commit clean.

## Caveat

Smoke covered Shadow-Hand-Over MAPPO. Other envs with different sensors
/ renderers / collision setups could surface warp 1.13 or mujoco 3.8
differences the smoke didn't exercise; full PR CI catches them.

---------

Co-authored-by: Kelly Guo <kellyg@nvidia.com>

## Summary

Bumps the Newton pin to
[`v1.2.0rc2`](https://pypi.org/project/newton/1.2.0rc2/), which pulls in
IsaacLab-relevant fixes plus the upstream tendon-scoping fix.

## What's new in Newton v1.2.0rc2 vs IsaacLab's current pin (`a27277e`)

The current IsaacLab Newton pin is from late April; v1.2.0rc2 is the
latest release-candidate cut. Notable fixes pulled in:

-
**[newton-physics/newton#2659](newton-physics/newton#2659
\"Scope USD custom-frequency parsing\" — `parse_usd` now scopes the
custom-frequency walk to `root_path` natively.
-
**[newton-physics/newton#2678](newton-physics/newton#2678
Regression fix.
-
**[newton-physics/newton#2720](newton-physics/newton#2720
`SolverKamino` reset under `world_mask`.
-
**[newton-physics/newton#2710](newton-physics/newton#2710
VRAM leak fix on example reset.
- Plus 16 other smaller fixes between rc1 and rc2.

## Required dep bumps

Newton 1.2.0rc2's \`pyproject.toml\` requires:

- \`warp-lang==1.13.0\`
- \`mujoco==3.8.0\` (was 3.6.0)
- \`mujoco-warp==3.8.0.1\` (was 3.6.0)

Pins updated in:

| File | Change |
|---|---|
| \`source/isaaclab/setup.py\` | \`warp-lang==1.12.0\` → \`==1.13.0\`;
\`mujoco==3.6.0\` → \`==3.8.0\`; \`mujoco-warp==3.6.0\` → \`==3.8.0.1\`
|
| \`source/isaaclab_newton/setup.py\` | mujoco / mujoco-warp bumps;
Newton pin → \`v1.2.0rc2\` |
| \`source/isaaclab_visualizers/setup.py\` | 3× Newton pin →
\`v1.2.0rc2\` |
| \`tools/wheel_builder/res/python_packages.toml\` | All four pins
mirrored |

## Code adapts

\`warp-lang\` 1.13 removed the \`wp.math\` namespace. Two IsaacLab call
sites use it:

-
\`source/isaaclab_newton/isaaclab_newton/physics/newton_manager.py:72\`
-
\`source/isaaclab_ov/isaaclab_ov/renderers/ovrtx_renderer_kernels.py:330\`

Both rewritten as \`wp.math.transform_to_matrix(...)\` →
\`wp.transform_to_matrix(...)\`. That's the only IsaacLab-side adapt
needed.

## Test plan

- [x] \`./isaaclab.sh -i newton\` clean install against the bumped pins.
- [x] \`pip list\` confirms \`newton 1.2.0rc2\`, \`warp-lang 1.13.0\`,
\`mujoco 3.8.0\`, \`mujoco-warp 3.8.0.1\`.
- [x] Sanity smoke: Shadow-Hand-Over MAPPO (4 envs, 1 iter) runs clean —
simulation init through CUDA graph capture through one training step +
checkpoint save, no errors.
- [x] Pre-commit clean.

## Caveat

Smoke covered Shadow-Hand-Over MAPPO. Other envs with different sensors
/ renderers / collision setups could surface warp 1.13 or mujoco 3.8
differences the smoke didn't exercise; full PR CI catches them.

---------

Co-authored-by: Kelly Guo <kellyg@nvidia.com>

After Newton's add_builder copies proto rows into the merged builder
for each environment, every row's label still references the source
proto path. Newton tracks env identity in *_world int companion
columns; IsaacLab keys data flow off USD prim paths, so each row's
label needs to be rewritten to its per-env destination path.

_rename_builder_labels now walks two kinds of label-bearing columns:

* Built-in label arrays (body, joint, shape, articulation,
  constraint_mimic, equality_constraint), each paired with its
  matching *_world int column.
* String-typed custom-attribute columns (e.g. mujoco:tendon_label)
  paired with a references="world" companion at the same frequency.
  Any future solver-registered string column at a frequency that has
  a references="world" companion is handled automatically.

The prefix match uses a path-separator boundary
(src_path.rstrip("/") + "/") so a source path that is a string
prefix of another (/Sources/protoA vs /Sources/protoAB) does not
cross-contaminate when both feed the same envs.

The function raises ValueError if the parallel arrays of labels and
worlds have mismatched lengths, instead of silently truncating.

Adds test_rename_builder_labels.py with 10 cases covering both
passes, multi-source prefix-overlap regression, sparse env ids,
multi-frequency, multiple string columns at one frequency, and
empty-values pass-through.

Stacks on top of isaac-sim#5523 (Newton v1.2.0rc2 bump). The Newton 1.2
release also includes upstream newton-physics/newton#2659 which
scopes parse_usd's custom-frequency walk natively, removing the
cross-source MjcTendon contamination IsaacLab previously had to
work around at the framework layer.

After Newton's add_builder copies proto rows into the merged builder
for each environment, every row's label still references the source
proto path. Newton tracks env identity in *_world int companion
columns; IsaacLab keys data flow off USD prim paths, so each row's
label needs to be rewritten to its per-env destination path.

_rename_builder_labels now walks two kinds of label-bearing columns:

* Built-in label arrays (body, joint, shape, articulation,
  constraint_mimic, equality_constraint), each paired with its
  matching *_world int column.
* String-typed custom-attribute columns (e.g. mujoco:tendon_label)
  paired with a references="world" companion at the same frequency.
  Any future solver-registered string column at a frequency that has
  a references="world" companion is handled automatically.

The prefix match uses a path-separator boundary
(src_path.rstrip("/") + "/") so a source path that is a string
prefix of another (/Sources/protoA vs /Sources/protoAB) does not
cross-contaminate when both feed the same envs.

The function raises ValueError if the parallel arrays of labels and
worlds have mismatched lengths, instead of silently truncating.

Adds test_rename_builder_labels.py with 10 cases covering both
passes, multi-source prefix-overlap regression, sparse env ids,
multi-frequency, multiple string columns at one frequency, and
empty-values pass-through.

Stacks on top of isaac-sim#5523 (Newton v1.2.0rc2 bump). The Newton 1.2
release also includes upstream newton-physics/newton#2659 which
scopes parse_usd's custom-frequency walk natively, removing the
cross-source MjcTendon contamination IsaacLab previously had to
work around at the framework layer.

…) (#5433)

## Summary

Extends `_rename_builder_labels` in
`isaaclab_newton.cloner.newton_replicate` so that every label-bearing
column on the merged Newton `ModelBuilder` is rewritten to per-env USD
paths after replication. Previously, only the built-in
body/joint/shape/articulation columns were rewritten; tendon labels (and
any other string-typed custom-attribute column) kept the source proto
path on every replicated environment.

## Stack / dependencies

- **Depends on #5523** (\"[Newton] Bump Newton pin to v1.2.0rc2\").
After #5523 lands, this PR rebases cleanly on develop.

The Newton 1.2 release
([newton-physics/newton#2659](newton-physics/newton#2659))
also includes the upstream tendon-scoping fix that obsoletes the
IsaacLab-side \`_scope_custom_frequencies\` workaround a previous
version of this PR carried — that workaround has been removed in favor
of relying on the Newton bump in #5523.

## Why the rename is needed

Newton's \`add_builder\` copies each proto's bodies, joints, shapes,
articulations, etc. into the merged builder verbatim, and tags each row
with a \`*_world\` integer column to track env identity. Labels (path
strings) are copied as-is. So after cloning N environments from one
proto, the merged builder has N copies of every row, all with the **same
proto-path string label**, distinguished only by the integer \`*_world\`
column.

IsaacLab keys most of its data flow off **USD prim paths** (sensor
binding, event-term scope, visualization, logging). It needs labels to
be unique per-env paths so a body called
\`/World/envs/env_3/Robot/Forearm\` is reachable by path lookup. The
rename function is the bridge: it walks every label-bearing column
post-replication and rewrites the source-root prefix to the per-env
destination root using each row's \`*_world\` value.

Until this PR, the rename only walked **5 built-in label arrays**.
Tendon labels and any string-typed custom-attribute column were missed,
so e.g. \`mujoco:tendon_label\` showed \`/World/envs/env_0/...\` for
every env — surfaced on Shadow Hand fixed tendons.

## What this PR changes

### \`_rename_builder_labels\` extension

* **Pass 1 (built-in label arrays)** — extended from 5 to 6 entity
types: \`body\`, \`joint\`, \`shape\`, \`articulation\`,
\`constraint_mimic\`, **\`equality_constraint\`** (the latter was
missing — would have surfaced for any env using \`MjcEquality\`
constraints, currently none).
* **Pass 2 (string custom-attribute columns)** — new. Walks every
registered custom attribute, finds string-typed columns whose frequency
has a \`references=\"world\"\` companion column, and applies the same
prefix rewrite. Any future solver-registered string column at such a
frequency is handled automatically without changes here.
* **Path-separator boundary** on the prefix match:
\`startswith(src_path.rstrip(\"/\") + \"/\")\`. Prevents source paths
that are string prefixes of one another (\`/Sources/protoA\` vs
\`/Sources/protoAB\`) from cross-contaminating when both feed the same
envs.
* **Hard error on length mismatch**: raises \`ValueError\` if the
parallel \`(labels, worlds)\` arrays differ in length, instead of
silently truncating. By contract Newton's \`add_builder\` keeps them in
lockstep.

### Tests

New \`source/isaaclab_newton/test/cloner/test_rename_builder_labels.py\`
with 10 cases covering:

- Both passes with built-ins and \`mujoco:tendon_label\` rewrite
correctly per world.
- Cross-pass consistency: every renamed label lives under the per-env
root.
- Guards: non-path strings pass through untouched; rows whose world id
is not in \`env_ids\` keep their original label.
- \`test_sparse_env_ids\` — non-contiguous env ids \`[10, 20, 30]\`.
- \`TestRenamePass2Generality\` — multiple coexisting custom
frequencies, multiple string columns at one frequency,
registered-but-empty string column.
-
\`TestRenameMultiSource::test_prefix_overlap_does_not_cross_contaminate\`
— explicit regression for the \`/Sources/protoA\` vs
\`/Sources/protoAB\` boundary fix; both sources feed the same envs so
the world-id guard cannot mask the boundary bug. Fails without the fix;
passes with it.

## Test plan

- [x] All 10 unit tests pass.
- [x] \`./isaaclab.sh -f\` clean (pre-commit hooks).
- [x] Verified the boundary-prefix regression test fails when the
boundary terminator is removed and passes when it's restored.
- [x] Smoke (Shadow-Hand-Over MAPPO 4 envs / iter 1) shows tendon labels
go from \`/World/envs/env_0/.../T_FFJ\` (every env) to
\`/World/envs/env_<wid>/.../T_FFJ\` (per-env paths) after the rename.

---------

Co-authored-by: Kelly Guo <kellyg@nvidia.com>