add n_jobs option to compute_nn_distances

[diegodoimo]

resolves #104

[codecov-commenter]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (bfbdb86) 80.36% compared to head (c7a0d4c) 79.71%.

Files	Patch %	Lines
dadapy/id_estimation.py	66.66%	2 Missing :warning:
dadapy/base.py	83.33%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #109 +/- ## ========================================== - Coverage 80.36% 79.71% -0.66% ========================================== Files 15 15 Lines 2491 2489 -2 ========================================== - Hits 2002 1984 -18 - Misses 489 505 +16 ```

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