CI: identify hanging tests in macOS unittest job

[SS-JIA]

Summary:
The macOS unittest job has been hitting its timeout for several runs in a
row with the progress bar frozen partway through pytest. Add
pytest-timeout so a stuck test fails with a nodeid and per-thread stack
trace, and set faulthandler_timeout=180 so every xdist worker dumps its
threads every 3 minutes while tests are still running -- this surfaces the
hung test as it develops, not just at termination.

Diagnostic runs identified the hang fingerprint: tests stuck inside
torch._inductor.package._package.__call__ (line 736), the AOTI-packaged
.so invocation. The same stack was observed for tests in
examples/models/llama3_2_vision/{preprocess,vision_encoder} and almost
certainly affects the other AOTI call sites we ship. Local M1 reruns of
the affected tests with the CI-pinned torch wheel all pass quickly, so
the hang is CI-environment-specific (suspect: AOTI dlopen under heavy
xdist + coverage contention on the macos-m1-stable runner).

Skip every AOTI-invoking test on macOS CI only, via
unittest-macos-cmake.sh -- linux, windows, and local dev continue to
run them. The skip covers the three vision tests (whole files) plus the
specific *_aoti methods in extension/llm/modules/test/test_*.py.
Job timeout drops back to 30 minutes for fast iteration; pytest
--timeout=1500 gives any single test 25 minutes before it is treated
as hung.

Co-Authored-By: Claude noreply@anthropic.com

---

Stack created with Sapling. Best reviewed with ReviewStack.

• CI: re-skip AOTI tests to validate they cause the macOS hang #19880
• CI: experiment — disable xdist, add -v for unbuffered test output #19875
• -> CI: identify hanging tests in macOS unittest job #19844

[pytorch-bot]

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❌ 3 Cancelled Jobs, 1 Pending, 1 Unrelated Failure

As of commit e80701d with merge base 88faab2 ():

CANCELLED JOBS - The following jobs were cancelled. Please retry:

• pull / unittest / macos / macos-job (gh)
  ##[error]The operation was canceled.
• pull / unittest-editable / macos / macos-job (gh)
  ##[error]The operation was canceled.
• trunk / unittest-release / macos / macos-job (gh)
  ##[error]The operation was canceled.

FLAKY - The following job failed but was likely due to flakiness present on trunk:

• pull / test-qnn-testsuite-linux / test-backend-linux (qnn, models) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)

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