Move flake8 config into pyproject

[oesteban]

Summary

• delete setup.cfg
• add [tool.flake8] section in pyproject.toml

Testing

• pip install .[tests]
• pytest -q (fails: FileNotFoundError in doctest)

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https://chatgpt.com/codex/tasks/task_e_6879d898c97883308912d343ad8072cf

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.98%. Comparing base (6b000c8) to head (1b544cb).
Report is 10 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #245      +/-   ##
==========================================
+ Coverage   94.84%   94.98%   +0.13%     
==========================================
  Files          16       16              
  Lines        1823     1833      +10     
  Branches      198      236      +38     
==========================================
+ Hits         1729     1741      +12     
+ Misses         77       76       -1     
+ Partials       17       16       -1     

Flag	Coverage Δ
unittests	94.84% <ø> (ø)

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