Normalize file modes stored in wheels

[fhgffy]

Fixes #362

WheelFile.write stored stat.S_IMODE from the build tree. That mode includes the process umask, so the same sources produced different wheels. Members are now stored as 0644, or 0755 when any execute bit is set.

Tests: pytest tests/test_wheelfile.py::test_write_normalizes_umask

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 63.57%. Comparing base (c4b173a) to head (1453049).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #702      +/-   ##
==========================================
+ Coverage   63.54%   63.57%   +0.02%     
==========================================
  Files          15       15              
  Lines        1270     1271       +1     
==========================================
+ Hits          807      808       +1     
  Misses        463      463              

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[fhgffy]

The failing test (ubuntu-latest, pypy-3.11") job is unrelated to this change. The matrix entry on main is missing its opening quote, so setup-python rejects the version. #703 fixes that.