Automate stable release dependency finalization

[JacobSzwejbka]

Summary

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

Review the artifact preflight first: the script derives final PyTorch, torchvision, and torchaudio versions from the RC train and verifies those packages together with TorchAO, pytorch-tokenizers, TorchCodec, and required submodule tags before editing. Then review the planned text and submodule updates, which finalize dependency pins and index URLs with rollback for partial failures. The wheel checks allow upstream RC dependencies for ExecuTorch RC tags but require a plain final PyTorch version and finalized dependencies for final ExecuTorch tags.

The script prepares a reviewable diff only. It does not commit, push, tag, publish wheels, or perform an ExecuTorch release.

Test plan

• python3 scripts/release/test_finalize_release.py (2 tests)
• mypy, ufmt, and flake8
• RC-to-final dependency promotion in an isolated checkout
• 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

Note: Links to docs will display an error until the docs builds have been completed.

❌ 1 New Failure, 2 Pending, 2 Unclassified Failures

As of commit 1b4c431 with merge base c5f2b7a ():

NEW FAILURE - The following job has failed:

• Build Presets / apple (pybind) / build (gh)
  RuntimeError: Command bash /Users/runner/work/_temp/exec_script failed with exit code 1

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 27ecd81a35d8fcb3c006c01710792d941145766350b3cad4f2acfbe06cee07c1 /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 135831dcbf64b63c9fbab6ac34b503bf83da1f06f3e6ed2c36194993f3ed0bed /exec failed with exit code 2

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