Feature/update prox

[michalk8]

closes #574

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.78%. Comparing base (ea7d5b9) to head (3c41171).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #575      +/-   ##
==========================================
+ Coverage   87.76%   87.78%   +0.01%     
==========================================
  Files          72       72              
  Lines        7791     7801      +10     
  Branches     1124     1126       +2     
==========================================
+ Hits         6838     6848      +10     
  Misses        802      802              
  Partials      151      151              

Files with missing lines	Coverage Δ
src/ott/geometry/costs.py	97.22% <100.00%> (+0.05%)	⬆️
src/ott/geometry/regularizers.py	98.65% <100.00%> (+0.01%)	⬆️

[marcocuturi]

Thanks a lot Michal!! mostly minor comments.

[pkassraie]

This PR effectively moves the regularization parameter $\lambda$ out of the signature for the regularization function, and attributes it to the overall loss, which I think makes more sense. This is done by adding the PostComposition class and updating the signatures. All good with me.

[pkassraie]

Just a pointer that the function definition of the overlap norm is the mathematical definition of the overlap norm divided by 2 (see line 418 of regularizers.py).