Stop free-threaded CI jobs failing in setup before tests run

[emeryberger]

Three matrix entries — run-tests (ubuntu-latest, 3.13t), (macos-latest, 3.13t) and (ubuntu-latest, 3.14t) — have been red without ever running pytest. In each, run tests shows as skipped because an earlier setup step aborted under bash -e.

Both causes are environment drift, not code: all four free-threaded jobs passed on master's 2026-07-05 run, and the failures reproduce identically on unrelated PRs (#1087, #1088).

3.13t — hypothesis can't be built for free-threaded 3.13

Building wheel for hypothesis (pyproject.toml): finished with status 'error'
    error: failed to run custom build command for `pyo3-ffi v0.29.0`
      error: PyO3 does not support the free-threaded build of CPython versions below 3.14,
             the selected Python version is 3.13

No wheel exists for cp313t, so pip builds from source and its dependency chain pulls pyo3-ffi. Installing it best-effort fixes the step.

That alone isn't sufficient. tests/test_runningstats.py and tests/test_scalene_json.py import hypothesis at module scope, and a collection error there interrupts the entire pytest session:

ERROR tests/test_runningstats.py
ERROR tests/test_scalene_json.py
!!!!!!!!!!! Interrupted: 2 errors during collection !!!!!!!!!!!

So both modules now call pytest.importorskip("hypothesis"), matching the convention already used for torch (test_torch_profiler.py) and numpy (test_issue1032_core_utilization_clamp.py).

3.14t — apt 404 on libc6-dbg

Err:9 mirror+file:/etc/apt/apt-mirrors.txt noble-updates/main amd64 libc6-dbg amd64 2.39-0ubuntu8.7
  404  Not Found [IP: 52.161.185.214 80]
E: Failed to fetch .../libc6-dbg_2.39-0ubuntu8.7_amd64.deb  404  Not Found
##[error]Process completed with exit code 100.

The runner image's package index is older than the mirror's contents. Adds apt-get update first, and stops a missing gdb from failing the job — gdb is only used by the optional Collect crash backtraces step, which is already || true guarded.

Verification

scenario	before	after
the two modules, hypothesis absent	Interrupted: 2 errors during collection, non-zero exit	2 skipped, exit 0
the two modules, hypothesis present	4 passed	4 passed (unchanged)
full suite locally	446 passed, 13 skipped	446 passed, 13 skipped

"hypothesis absent" was exercised in a real venv without the package, not simulated. The apt change can only be exercised on an Ubuntu runner, so this PR's own 3.14t job is the test.

Note, not addressed here

ulimit -c unlimited runs in its own step, and each run: block is a separate shell, so it doesn't apply to the later pytest step — core dumps likely were never actually enabled, which would leave Collect crash backtraces with nothing to find. Fixing that means restructuring where the limit is set, which is beyond this PR's scope of un-breaking the setup steps.

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