tests/test_flash_attn.py fails collection without einops

Reproduction

At commit 0251105a2fb19d2957484b7f023cd8c115286ced, from the repository root on Linux with Python 3.14 and pytest available:

$ PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 pytest -q -s tests/test_flash_attn.py

Actual result

Collection stops before any FlashAttention test runs:

tests/test_flash_attn.py:6: in <module>
    from einops import rearrange, repeat
E   ModuleNotFoundError: No module named 'einops'

Expected result

The source-test prerequisites should provide einops, or the test instructions should explicitly name the dependency installation needed before this command can collect.

Issue #961 reports the same import symptom for a source installation. This report is specifically the reproducible failure of the current repository test entrypoint and the missing test-prerequisite declaration.