[MRG] Proximal point solver for batched optimal transport

[thibaut-germain]

Types of changes

Implementation of the Bregman divergence based proximal point solver for optimal transport.

Motivation and context / Related issue

Provide differentiable approximation of exact optimal transport plans computed in parallel.

How has this been tested (if it applies)

New tests implemented in test/batch/test_solve_batch.py. Tests on all configurations possible and transport plan accuracy.

PR checklist

• [ x] I have read the CONTRIBUTING document.
• [ x] The documentation is up-to-date with the changes I made (check build artifacts).
• [ x] All tests passed, and additional code has been covered with new tests.
• [ x] I have added the PR and Issue fix to the RELEASES.md file.

[rflamary]

Neraly there @thibaut-germain could you update the example file?

[codecov]

Codecov Report

❌ Patch coverage is 97.60000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.86%. Comparing base (c836b97) to head (f7e82ac).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #832   +/-   ##
=======================================
  Coverage   96.85%   96.86%           
=======================================
  Files         128      128           
  Lines       25593    25659   +66     
=======================================
+ Hits        24788    24854   +66     
  Misses        805      805           

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.