CI: test job can hang 90 min when HuggingFace download stalls during pytest collection

Summary

A CI test job can hang for the full timeout-minutes: 90 and end as "The operation was canceled" when the HuggingFace download of angle.onnx stalls during pytest collection, where pytest-timeout offers no protection.

Evidence (run 29286008697, job run_tests (3.14) on PR #1059)

• All three matrix jobs started simultaneously; 3.12 and 3.13 passed in ~8.5 min. Only 3.14 hung.
• The job log's last activity before an 89-minute silence:

21:22:04 ----------------------------- live log collection ------------------------------
21:22:05 INFO httpx: HEAD https://huggingface.co/franklab/HSSM/resolve/main/angle.onnx "HTTP/1.1 302 Found"
21:22:05 WARNING huggingface_hub: You are sending unauthenticated requests to the HF Hub...
22:51:25 ##[error]The operation was canceled.

• Runner cleanup shows orphaned uv and pytest processes — a hang, not a crash. The workflow-level timeout-minutes: 90 is what killed it.
• The same code (docstring-only diff) passed CI 15 minutes earlier, so this is a network flake, not a code issue.

Root cause

tests/rl/test_rl_likelihood_builder.py:33 calls make_jax_matrix_logp_funcs_from_onnx(...) at module level, so the HF download runs at import/collection time. Verified with HF_HUB_OFFLINE=1 HF_HOME=<empty> pytest --collect-only, which errors at exactly that line. pytest-timeout (360s, signal) only guards test execution, not collection — a stalled CDN connection during collection hangs the job until the 90-minute workflow timeout.

Suggested fixes

1. Move the module-level network download in tests/rl/test_rl_likelihood_builder.py into a (module-scoped) fixture so it runs under test setup, where pytest-timeout applies — or use the local tests/fixtures/angle.onnx like tests/distribution_utils/ does.
2. Set HF_TOKEN (repo secret) in the test workflow env — unauthenticated requests get throttled and are the likely stall trigger.
3. Cache ~/.cache/huggingface with actions/cache keyed on the network artifact list, so matrix jobs don't re-download at all.
4. Optionally set HF_HUB_DOWNLOAD_TIMEOUT (e.g. 30) in the workflow env so a stalled download raises quickly instead of hanging.

🤖 Generated with Claude Code

Start with tests/rl/test_rl_likelihood_builder.py:33 and the test workflow's timeout and environment settings. Run the documented HF_HUB_OFFLINE=1 pytest --collect-only check, then inspect how tests/distribution_utils/ handles the local angle.onnx fixture. Done means pytest collection no longer hangs on the network download and the affected CI job completes within its configured timeout.