Fix pickle cache rewrite races

[shaypal5]

Summary

• make shared pickle-cache rewrites atomic with a temp file plus os.replace
• use a sidecar lockfile outside cache directories for shared pickle-cache reads and writes so Windows can replace cache files safely
• handle moved filesystem events in the pickle watchdog path
• add regression coverage for concurrent shared-cache rewrites

Context

• fixes the macOS cleanup failure in tests/test_cleanup.py::test_cleanup_stale_entries
• fixes the Windows smoke-test regression from replacing an open cache file
• preserves expected cache-directory contents for separate_files=True and separate_files=False

Files

• src/cachier/cores/pickle.py
• tests/pickle_tests/test_pickle_core.py

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.94%. Comparing base (98f137b) to head (3cdd940).

Additional details and impacted files

@@             Coverage Diff             @@
##            master     #364      +/-   ##
===========================================
- Coverage   100.00%   99.94%   -0.06%     
===========================================
  Files           12       12              
  Lines         1701     1731      +30     
  Branches       213      216       +3     
===========================================
+ Hits          1701     1730      +29     
- Partials         0        1       +1     

Flag	Coverage Δ
local	59.21% <100.00%> (+0.66%)	⬆️
mongodb	40.55% <17.64%> (-0.37%)	⬇️
postgres	43.44% <17.64%> (-0.42%)	⬇️
redis	46.67% <17.64%> (-0.48%)	⬇️
s3	42.46% <17.64%> (-0.40%)	⬇️

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Files with missing lines	Coverage Δ
src/cachier/cores/pickle.py	99.65% <100.00%> (-0.35%)	⬇️

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[Copilot]

Pull request overview

Bumps the Cachier package version to 4.3.0 for the v4.3.0 release.

Changes:

• Updated the version string from 4.2.0 to 4.3.0

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.