Refactor `local_weighted_learning.py` to use `np.array` (#8069)

* updating DIRECTORY.md

* Format local_weighted_learning.py doctests for clarity

* Refactor local_weighted_learning.py to use np.array instead of np.mat

The np.matrix class is planned to be eventually depreciated in favor of
np.array, and current use of the class raises warnings in pytest

* Update local_weighted_learning.py documentation

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