Added support for specifying threads/cpu (default 1 per CPU) to address issue #1162. Only affects a subset of the functions for usearch61 OTU picking and chimera checking. Also fixed a non-related order-dependent error in tests/test_pick_otus.py
Changed docstrings per Greg's request
fixed indent
Merge pull request #1265 from walterst/usearch_remove_multithreading2

Added support for specifying threads/cpu (default 1 per CPU) to address ...