Adding conditional monge gap

[DriessenA]

For now we've only implemented cmonge_gap_from_samples, we will follow with a ConditionalMongeGapEstimator.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 75 lines in your changes missing coverage. Please review.

Project coverage is 87.06%. Comparing base (e6fff13) to head (b94fef6).

Files with missing lines	Patch %	Lines
...eural/networks/conditional_perturbation_network.py	0.00%	45 Missing ⚠️
src/ott/neural/methods/conditional_monge_gap.py	0.00%	30 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #605      +/-   ##
==========================================
- Coverage   87.91%   87.06%   -0.86%     
==========================================
  Files          74       76       +2     
  Lines        7657     7731      +74     
  Branches      533      539       +6     
==========================================
- Hits         6732     6731       -1     
- Misses        783      858      +75     
  Partials      142      142              

Files with missing lines	Coverage Δ
src/ott/neural/methods/conditional_monge_gap.py	0.00% <0.00%> (ø)
...eural/networks/conditional_perturbation_network.py	0.00% <0.00%> (ø)

... and 1 file with indirect coverage changes