Refactor/handle solve args

[selmanozleyen]

hi @MUCDK ,

So good news is we currently do a good job on partitioning the kwargs for solve. In solve we give any kwarg we don't know to either SinkhornSolver or GWSolver constructors. SinkhornSolver uses Sinkhorn or LRSinkhorn from ottjax, these classes don't have kwargs in their constructors so when using SinkhornSolver as a backend we are good. GWSolver uses GromovWasserstein or LRGromovWasserstein from ottjax. The parent class of these class WassersteinSolver don't throw an error on unrecognized args. The tests will pass after the ottjax PR merges.

Here is the PR in ott-jax: https://github.com/ott-jax/ott/pull/579

Other things done:

• Added tests if we throw appropriate errors on completely unrecognized arguments
• I refactored where we handle checks for alpha, now it's completely independent from CompoundProblem or any other more abstract class. It's handled in GWSolver as it should.
• I added extra tests on the errors we raise for alpha or the data given.

Additionally closes:

• turns out we can remove the skip for these test so I will close https://github.com/theislab/moscot/issues/678
• https://github.com/theislab/moscot/issues/703
• https://github.com/theislab/moscot/issues/720