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.