Support for scipy 1.14

[andr-kun]

PR Checklist

• Referenced issue is linked
• If you've fixed a bug or added code that should be tested, add tests!
• Documentation in docs is updated

Description of changes

The new scipy version (1.14+) deprecate the use of .A to access the array value of sparse matrices, which breaks some functions within pertpy. This PR fixes the issue by using the toarray() function to access the array value of sparse matrices.

Technical details

The PR fix works on both the new scipy version (1.14+) and older scipy version (1.13.1) as well. However, I was only able to test the guide RNA and milo functions, not the discriminator classifier function.

[Zethson]

Dear @andr-kun

thank you! I'm surprised that we haven't run into that in our CI yet. Maybe one of our dependencies bounded scipy?

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 16.66667% with 5 lines in your changes missing coverage. Please review.

Project coverage is 66.99%. Comparing base (c4233dd) to head (a9aac89).
Report is 1 commits behind head on main.

Files	Patch %	Lines
pertpy/preprocessing/_guide_rna.py	0.00%	4 Missing ⚠️
pertpy/tools/_milo.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #646      +/-   ##
==========================================
+ Coverage   64.43%   66.99%   +2.55%     
==========================================
  Files          46       46              
  Lines        5942     5942              
==========================================
+ Hits         3829     3981     +152     
+ Misses       2113     1961     -152     

Files	Coverage Δ
.../_perturbation_space/_discriminator_classifiers.py	89.26% <100.00%> (ø)
pertpy/tools/_milo.py	61.03% <0.00%> (ø)
pertpy/preprocessing/_guide_rna.py	50.00% <0.00%> (ø)

... and 4 files with indirect coverage changes