Use precomputed clustering

[mumichae]

Improve performance of clustering function to reduce redundant kNN and clustering operations

• cluster_optimal_resolution will not rerun sc.pp.neighbors or clustering by default if cluster key exists for the specified resolution (by name matching)`
• update get_resolutions function to scale equally between 0 and n

[codecov]

Codecov Report

Attention: Patch coverage is 96.96970% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 58.16%. Comparing base (127e41e) to head (2b3230d).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #406      +/-   ##
==========================================
+ Coverage   57.85%   58.16%   +0.31%     
==========================================
  Files          22       22              
  Lines        1675     1683       +8     
==========================================
+ Hits          969      979      +10     
+ Misses        706      704       -2     

Flag	Coverage Δ
unittests	58.16% <96.96%> (+0.31%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
scib/metrics/isolated_labels.py	93.65% <100.00%> (+0.66%)	⬆️
scib/metrics/clustering.py	88.34% <96.15%> (+2.21%)	⬆️