Currently, our trampoline is used to convert `<command> [args]` to
`python <command> [args]` for script entrypoints installed into virtual
environments. For #8458, it'd be nice to convert a shim `python3.12
[args]` to `python [args]`. Here, we modify the trampolines to support
this use-case.

The only change we really need here is to avoid injecting `<command>`
into the child process. We change the "magic number" at the end of the
trampoline executables from `UVUV` to `UVSC` and `UVPY` which define
"script" and "python" variants to the trampoline. We then omit the
`<command>` injection in the latter case. We also omit writing the zip
script payload.

To support construction of the new variant, a new
`uv-trampoline-builder` crate is introduced — this avoids requirements
on `uv-install-wheel` in future work. I also use `uv-trampoline-builder`
to consolidate some of the test setup for `uv-trampoline`.

There should be no backwards compatibility concerns, since trampolines
are fully self-referential.

I rebased to fix the commits at the end, as this took many iterations to
get working via CI. This should roughly be reviewable by commit if you
prefer.

Currently, our trampoline is used to convert `<command> [args]` to
`python <command> [args]` for script entrypoints installed into virtual
environments. For #8458, it'd be nice to convert a shim `python3.12
[args]` to `python [args]`. Here, we modify the trampolines to support
this use-case.

The only change we really need here is to avoid injecting `<command>`
into the child process. We change the "magic number" at the end of the
trampoline executables from `UVUV` to `UVSC` and `UVPY` which define
"script" and "python" variants to the trampoline. We then omit the
`<command>` injection in the latter case. We also omit writing the zip
script payload.

To support construction of the new variant, a new
`uv-trampoline-builder` crate is introduced — this avoids requirements
on `uv-install-wheel` in future work. I also use `uv-trampoline-builder`
to consolidate some of the test setup for `uv-trampoline`.

There should be no backwards compatibility concerns, since trampolines
are fully self-referential.

I rebased to fix the commits at the end, as this took many iterations to
get working via CI. This should roughly be reviewable by commit if you
prefer.

Following #8458, we need to remove the installed Python executables on
`uv python uninstall`.

Needs Windows support still, but that approach will be different since
there won't be links.

Following #8458 we want to support showing the target directory in the
CLI

Following #8458, we need to remove the installed Python executables on
`uv python uninstall`.

Needs Windows support still, but that approach will be different since
there won't be links.

Following #8458 we want to support showing the target directory in the
CLI

Following #8458, we need to remove the installed Python executables on
`uv python uninstall`.

Needs Windows support still, but that approach will be different since
there won't be links.

Following #8458 we want to support showing the target directory in the
CLI