Add Decipher Trajectory methods

[justjhong]

Implements the methods that require a pre-computed trajectory onto the Decipher model class.

cc @ANazaret

[codecov]

Codecov Report

Attention: Patch coverage is 95.89041% with 3 lines in your changes missing coverage. Please review.

Please upload report for BASE (jhong/deciphermethods@a5c3487). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
src/scvi/external/decipher/_model.py	93.10%	2 Missing ⚠️
src/scvi/external/decipher/utils/_trajectory.py	97.56%	1 Missing ⚠️

Additional details and impacted files

@@                   Coverage Diff                    @@
##             jhong/deciphermethods    #3092   +/-   ##
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  Coverage                         ?   84.71%           
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  Files                            ?      181           
  Lines                            ?    15259           
  Branches                         ?        0           
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  Hits                             ?    12927           
  Misses                           ?     2332           
  Partials                         ?        0           

Files with missing lines	Coverage Δ
src/scvi/external/decipher/utils/__init__.py	100.00% <100.00%> (ø)
src/scvi/external/decipher/utils/_rotate.py	87.50% <ø> (ø)
src/scvi/external/decipher/utils/_trajectory.py	97.56% <97.56%> (ø)
src/scvi/external/decipher/_model.py	96.11% <93.10%> (ø)

[canergen]

LGTM. See two point above, fix pre-commit missing empty line and add CHANGELOG.