Fix distance computation in umap_metrics.py

[lorenz-gorini]

In umap_metrics.py module many functions can be found with very similar purpose and naming.
For example gower_dist_numerical_old and gower_dist_numerical are different implementations meant to compute Gower distance between two vectors.
Similarly the module contains tanimoto_gower, tanimoto_gower_old and tanimoto_gower_no_bool_weights.

My proposal is to accurately check the appropriate algorithm that can compute tanimoto-gower distance in an efficient way, and verify its results with tests in test_metrics.py.

HINT: tanimoto_gower and gower_dist_numerical do not seem to be working perfectly, but according to previous comparisons, they seem to lead to better results.