… barrels; fix #9806, #9691, #9964

Add `experimental.wrappedModuleTreeshaking` (off by default), a new side-effect
tree-shaking implementation for wrapped ESM modules. The legacy impl force-includes
a wrapped `sideEffects:false` re-export barrel; the new impl prunes it — the used
binding's canonical owner is initialized via the binding-use path, and the finalizer
follows canonical owners when a barrel is pruned.

A module is wrapped (WrapKind::Esm) by many triggers — strictExecutionOrder,
require(esm), code-splitting / CJS interop — so this gate is the legacy-vs-new switch
for ALL wrap paths, not just strictExecutionOrder. It fixes the #9961 family of
over-retention / dangling-init ReferenceErrors.

Safety guards (so flag-on never produces broken output):
- namespace-taint: weakly-connected import components containing a star-import edge
  revert to legacy wrapping (prevents included-but-empty wrapped modules /
  code-splitting panics; member-resolution-aware pruning is future work).
- external-barrel: never prune a barrel that directly imports from an external module
  (its import would be dropped while still referenced).
- off by default => byte-identical legacy output.

Also fix #9806, #9691, #9964 (lazyBarrel, default-on) — one root cause: lazyBarrel
deferred an import record whose binding is read by a retained statement of a wrapped
module (a barrel-own `const Bar = Foo.Bar;` for #9806; a re-exported `sideEffects:false`
leaf's top-level read for #9691/#9964), so the finalizer dropped the import declaration
while the reading statement survived => ReferenceError. The loader now force-loads any
such record (BarrelState::initialize_barrel_tracking), keeping the import and
initializing it before the read. This also removes the lazyBarrel crash-layer of #9961.
(#9691 supersedes the correctness goal of PR #9709; its dead-star-source pruning is now
reachable via the wrappedModuleTreeshaking flag — see the #9691 flag variant snapshot.)

Plumbing: ExperimentalOptions + napi binding + TS type/validator/bindingify +
config-variant test support + auto-regenerated schema. A shadow-mode diagnostic pass
(init_obligations.rs, env-gated by ROLLDOWN_DUMP_INIT_OBLIGATIONS) validates the model
without affecting output.

Tests: node-executed regression fixtures — #9961 (bug/fix), #9964 (require(esm) wrap)
and #9691 (codeSplitting:false wrap; flag variant prunes the dead star source), each
verified necessary (crashes on the parent commit with the documented ReferenceError,
passes here), exports_chain prune, namespace-taint revert, per-binding activation,
side-effect soundness, external-barrel guard, #9806, and a non-strict require(esm)
witness. Full integration suite green.

Design: internal-docs/linking/strict-execution-order-rewrite-proposal.md