new tests to check jacobian, small fixes in: transport interface, handling of kernel_ridge in implicit differentiation of sinkhorn

In this release:

• more tests to check accuracy of differentiation of the optimal potentials w.r.t. input parameters.
• fixes issues in transport.Transport handling of **kwargs, that must be routed to the epsilon_scheduler object.
• cancel ridge_kernel in the unbalanced case when doing implicit differentiation.