feat(train) Add support for categorial covariates in scArches

[ori-kron-wis]

closes https://github.com/scverse/scvi-tools/issues/2583

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 85.31%. Comparing base (b9d839d) to head (e1830a3). Report is 53 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2936   +/-   ##
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  Coverage   85.31%   85.31%           
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  Files         167      167           
  Lines       14388    14386    -2     
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- Hits        12275    12274    -1     
+ Misses       2113     2112    -1     

Files with missing lines	Coverage Δ
src/scvi/model/base/_archesmixin.py	92.07% <100.00%> (-0.10%)	:arrow_down:

... and 1 file with indirect coverage changes

[canergen]

Can you please run https://docs.scvi-tools.org/en/1.0.2/tutorials/notebooks/scarches_scvi_tools.html with adding categorical covariate key in addition to the batch key and by replacing batch_key with categorical covariate key and verify that the results are the same?

[ori-kron-wis]

Results were the same