Switch to src based repository structure

[maxnoe]

Immediate issue:

Since all files were moved, they were all "touched" in this PR, which triggered the pre-commit hook to reformat all files.

So they are not just moved but also reformatted.

[maxnoe]

But actually the changes are very small, so maybe not that large of an issue

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (d0ed459) 92.52% compared to head (5d2aa9e) 92.52%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2459      +/-   ##
==========================================
- Coverage   92.52%   92.52%   -0.01%     
==========================================
  Files         234      234              
  Lines       20006    20005       -1     
==========================================
- Hits        18511    18510       -1     
  Misses       1495     1495              

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[Tobychev]

Missing a changelog, and I don't feel able to review the dark magic in setup.cfg, otherwise it looks fine

[maxnoe]

Missing a changelog, and I don't feel able to review the dark magic in setup.cfg, otherwise it looks fine

See setuptools documentation: https://setuptools.pypa.io/en/latest/userguide/package_discovery.html#package-discovery-and-namespace-packages