[MRG] BAPG solvers for GW and FGW

[cedricvincentcuaz]

Types of changes

• Add Bregman alternated projected gradient solvers for GW and FGW via functions: BAPG_gromov_wasserstein, BAPG_gromov_wasserstein2, BAPG_fused_gromov_wasserstein, BAPG_fused_gromov_wasserstein2

• update example with FGW solvers comparison.

Motivation and context / Related issue

• Keep up with the (F)GW literature.

How has this been tested (if it applies)

• add tests test_BAPG_fgw, test_BAPG_gromov. Modified in place test_entropic_gromov_dtype_device, test_entropic_fgw_dtype_device.

PR checklist

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

[codecov]

Codecov Report

Merging #581 (655a95e) into master (f809253) will increase coverage by 0.05%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #581      +/-   ##
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+ Coverage   96.66%   96.71%   +0.05%     
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  Files          75       75              
  Lines       15416    15651     +235     
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+ Hits        14902    15137     +235     
  Misses        514      514