Fix for #2887, update Leiden and Louvain tools to write parameters to user specified key

[theJasonFan]

Fix for #2887. Updated and added basic tests to Leiden and Louvain clustering to check that the parameters are written to the user specified key.

• [x] Closes #2887
• [x] Tests included

• [ ] Release notes not necessary because

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 50.00000% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 73.22%. Comparing base (360e350) to head (4bc1c48).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2889      +/-   ##
==========================================
- Coverage   74.92%   73.22%   -1.71%     
==========================================
  Files         116      116              
  Lines       12802    12765      -37     
==========================================
- Hits         9592     9347     -245     
- Misses       3210     3418     +208     

Files	Coverage Δ
scanpy/tools/_leiden.py	88.40% <100.00%> (ø)
scanpy/tools/_louvain.py	21.42% <0.00%> (ø)

... and 26 files with indirect coverage changes

[ilan-gold]

@ivirshup Can we stick this in 1.10? It seems small enough and IMO basically constitutes a breaking change anyway. then @theJasonFan can add a release note and we can merge if we don't notice anything else wrong here.