Automate stable release dependency finalization

[JacobSzwejbka]

Summary

Follow-up to #23287. This keeps stable dependency finalization separate from branch-cut preparation.

Candidate package versions are already final-form on the PyTorch test index. Finalization therefore verifies that Torch, torchvision, and torchaudio have reached PyPI and that their cu134 variants exist on the stable PyTorch index; it does not invent or remap companion versions. It switches installs from the test index to stable, moves the PyTorch source pin and vendored c10 headers from the newest RC tag to the final vX.Y.Z tag, finalizes TorchAO, pytorch-tokenizers, TorchCodec and submodule tags, and marks the branch finalized. All planned text, source, and submodule changes are covered by rollback.

Final ExecuTorch tags require the finalized marker and a plain final Torch version. The script prepares a reviewable diff only: it does not commit, push, tag, publish wheels, or perform an ExecuTorch release.

Test plan

• finalization suite: 2 tests
• combined preparation and finalization pytest collection: 4 tests
• mypy, ufmt, flake8, and git diff --check

Authored with OpenAI Codex.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/23289

• 📄 Preview Python docs built from this PR

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❌ 1 Pending, 2 Unclassified Failures

As of commit 3eb605e with merge base c5f2b7a ():

UNCLASSIFIED FAILURES - DrCI could not classify the following jobs because the workflow did not run on the merge base. The failures may be pre-existing on trunk or introduced by this PR:

• Test ROCm AOTI / test-voxtral-realtime-rocm-gfx950-rocm7.2 / linux-job (gh) (this job did not run on the merge base, so DrCI cannot tell whether the failure is pre-existing)
  RuntimeError: Command docker exec -t a5bfaea7d804ae4182c28a5baeb28d6d477ee54e213aaa81208396257635cce9 /exec failed with exit code 2
• Test ROCm AOTI / unittest-rocm-gfx950-rocm7.2 / linux-job (gh) (this job did not run on the merge base, so DrCI cannot tell whether the failure is pre-existing)
  RuntimeError: Command docker exec -t e7e599b8cba025330308a620149ac086df6f8dd18d22cb0b3ccfdada1d5f074d /exec failed with exit code 2

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