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. Drop the job timeout to
30 minutes so we can iterate quickly on this diagnostic loop.

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

[pytorch-bot]

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❌ 3 Cancelled Jobs, 310 Pending, 3 Unclassified Failures

As of commit eb38dd3 with merge base b903c30 ():

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:

• Build Aarch64 Linux Wheels / generate-matrix / generate (gh) (this job did not run on the merge base, so DrCI cannot tell whether the failure is pre-existing)
• Build Linux Wheels / generate-matrix / generate (gh) (this job did not run on the merge base, so DrCI cannot tell whether the failure is pre-existing)
• periodic / gather-models (gh) (this job did not run on the merge base, so DrCI cannot tell whether the failure is pre-existing)

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

• Test XNNPACK Backend / test-xnnpack / package-golden-artifacts (gh)
• Test XNNPACK Backend / test-xnnpack / test-backend-linux (xnnpack, models) / linux-job (gh)
• Test XNNPACK Backend / test-xnnpack / test-backend-linux (xnnpack, operators) / linux-job (gh)

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[linux-foundation-easycla]

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[SS-JIA]

Accidental duplicate from sl pr submit after amend broke PR linkage. Real PR is #19844.