Fix ARM test listing failures caused by torch import at collection time (#20284)

[Gasoonjia]

Summary:

The ~180 ARM test listings fail in fbcode//mode/opt during pytest
collection with AttributeError: module 'torch' has no attribute '_utils'.

Root cause: torch._utils is importable but is not bound as an attribute on
the torch module, so importing torch._dynamo (pulled in via
executorch.exir / torchao when a test module is collected) reads
torch._utils directly and crashes the whole listing. This is independent of
the seed call and of CinderX lazy imports (already disabled for these targets,
verified at runtime).

The previous version guarded the early seed with try/except, which neither set
the seed internally nor actually fixed the listings (the crash originates in
test-module collection, not the seed call).

Fix: bind torch._utils explicitly in _set_random_seed(), which runs in
pytest_configure before collection, and drop the try/except so the
collection-time seeding from D108449705 is restored. The change is identical
for OSS and internal (a no-op where torch._utils is already bound), which
also addresses the reviewer ask to seed the same way for both.

Verified in fbcode//mode/opt: fixes ~170/180 listings and re-enables the
collection-time seed.

Known follow-up (T275980003): ~10 targets that import
torchao.prototype.mx_formats still fail on torch.device unbound during
torchao's import-time device probing — a separate torch/torchao issue.

Reviewed By: shoumikhin

Differential Revision: D108630941

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/20284

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❌ 3 New Failures

As of commit 93b32b3 with merge base e257a71 ():

NEW FAILURES - The following jobs have failed:

• pull / test-multimodal-linux (gemma3-4b) / linux-job (gh)
  RuntimeError: Command docker exec -t 1705e63eac5fc08855554d9642851c9623aefb7bc17ce406403d2ce26c25d263 /exec failed with exit code 139
• pull / unittest / windows / windows-job (gh)
  examples/models/test/test_export.py::ExportTest::test_efficient_sam_export_to_executorch
• Test QNN Backend / test-qnn / test-backend-linux (qnn, models) / linux-job (gh)
  RuntimeError: Command docker exec -t 1b0b3c826bfd6f93490b3f774ae525391564135b624181aee3930ce821cbaf9f /exec failed with exit code 92

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[meta-codesync]

@Gasoonjia has exported this pull request. If you are a Meta employee, you can view the originating Diff in D108630941.

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