Types of changes

This PR is dedicated to the implementation of
1.Fused Unbalanced GW (or more correctly, its lower bound)
2. (Fused) Unbalanced COOT.

Since their structures, it is enough to write a common template, then write a wrapper for each divergence.
More precisely, we create a method called fused_unbalanced_cross_spaces_divergence , in which

• reg_type="independent" corresponds to (Fused) UCOOT. This yields unbalanced_co_optimal_transport method.
• reg_type="joint" corresponds to FUGW. This yields fused_unbalanced_gromov_wasserstein method.

We also allow for unregularized approximation of FUGW and UCOOT, i.e.