[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 (99477be) to head (27c5009).

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     

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.