[MRG] Fix None init plan in unbalanced lbfgs solvers

[cedricvincentcuaz]

Types of changes

fix undesirable behaviour of ot.unbalanced.lbfgsb_unbalanced when isinstance(reg_div, tuple) to test whether included functions in reg_div can handle numpy arrays. These tests are now handled via ot.utils.fun_to_numpy.

Motivation and context / Related issue

How has this been tested (if it applies)

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

All modified and coverable lines are covered by tests ✅

Project coverage is 97.10%. Comparing base (2825682) to head (3ec9057).
Report is 1 commits behind head on master.

Additional details and impacted files

@@ Coverage Diff @@ ## master #731 +/- ## ======================================= Coverage 97.09% 97.10% ======================================= Files 100 100 Lines 20432 20453 +21 ======================================= + Hits 19839 19861 +22  + Misses 593 592 -1 

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