introduce sinkdiv simplified API, expand glossary with sinkhorn divergence and LR sinkhorn

[marcocuturi]

This PR introduces a few enhancements:

• introduces a sinkdiv convenience wrapper to compute the Sinkhorn divergence between two point clouds. Using the sinkhorn_divergence method was a bit clumsy in that case, since it required passing first the PointCloud geometry type, clearly overkill for most usages.

• introduces the possiblity to store the reg_ot_cost between the second point cloud (in a sinkhorn divergence) and itself and use it as an offset. This is useful when one wants to track the true Sinkhorn divergence between two point clouds but do not want to recompute that term at every iteration, say, of a Gradient descent. that quantity is calledoffset_static_b

• corrects a bug in the plot class, whereby titles were ignored when the show_lines flag was False

• expands glossary.rst

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Codecov Report

Attention: Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.

Project coverage is 88.17%. Comparing base (828acca) to head (b7f8624).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/ott/tools/plot.py	75.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #596      +/-   ##
==========================================
+ Coverage   88.13%   88.17%   +0.04%     
==========================================
  Files          73       73              
  Lines        7768     7770       +2     
  Branches      556      556              
==========================================
+ Hits         6846     6851       +5     
+ Misses        779      778       -1     
+ Partials      143      141       -2     

Files with missing lines	Coverage Δ
src/ott/solvers/linear/sinkhorn_lr.py	98.98% <ø> (ø)
src/ott/tools/sinkhorn_divergence.py	94.31% <100.00%> (+2.45%)	⬆️
src/ott/tools/plot.py	54.09% <75.00%> (ø)

... and 1 file with indirect coverage changes