Narrow cache load exception handler

[johmathe]

Summary

• Replace bare except Exception in _load_sparse_cache with explicit (OSError, RuntimeError, KeyError, pickle.UnpicklingError)
• Avoids silently swallowing unexpected errors while still handling all known corruption/incompatibility cases

Test plan

• pytest tests/test_coverage_gaps.py::TestSO3SparseCacheIO — 5 passed

Made with Cursor

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.50%. Comparing base (b1111a2) to head (712ffa8).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #46   +/-   ##
=======================================
  Coverage   95.50%   95.50%           
=======================================
  Files          11       11           
  Lines        2134     2135    +1     
=======================================
+ Hits         2038     2039    +1     
  Misses         96       96           

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