Split cache cleanup test assertions with weakrefs

[pjbull]

Summary

• Cache cleanup tests now prove objects were garbage collected via weak references before polling for file removal.
• Failures distinguish a still-referenced object (so __del__ could not run) from filesystem lag or a real cleanup bug.
• Replaces the broad retry in test_manual_cache_clearing that mixed gc.collect() with exists() checks.

Test plan

• Mocked suite: make test — 1111 passed, 18 skipped
• Live backends: USE_LIVE_CLOUD=1 make test-live-cloud — 1116 passed, 13 skipped
• CI green on Linux, macOS, and Windows

Made with Cursor

[github-actions]

🚀 Deployed on https://deploy-preview-587--gallant-agnesi-5f7bb3.netlify.app

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.4%. Comparing base (9df4281) to head (8ad07b7).

Additional details and impacted files

@@          Coverage Diff           @@
##           master    #587   +/-   ##
======================================
  Coverage    94.4%   94.4%           
======================================
  Files          28      28           
  Lines        2290    2290           
======================================
  Hits         2164    2164           
  Misses        126     126           

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