Change default matplotlib.rcParams["axes.grid"] from True to False

[senseibence]

Description

When creating heatmaps, matrices, and various graphs using large datasets with seaborn, scanpy.set_figure_params() provides helpful default configurations for the plot. However, one default, caused by matplotlib.rcParams["axes.grid"] = True, provides no benefit to the vast majority of plots, making them unreadable and confusing (especially with very large plots). Below is a simple example; evidently, the distortion increases with graph complexity.

Images

Graph with default grid:

Graph without default grid:

Conclusion

This change simply modifies matplotlib.rcParams["axes.grid"] from True to False, not affecting any other components of the module. We believe this adjusted default would benefit the majority of graphs compared to the original. If one would like to use the grid lines for any reason (which we believe is a niche use case), they may run matplotlib.pyplot.rcParams["axes.grid"] = True.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.59%. Comparing base (d0adc25) to head (7562ad2).
Report is 56 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3347   +/-   ##
=======================================
  Coverage   76.59%   76.59%           
=======================================
  Files         111      111           
  Lines       12827    12827           
=======================================
  Hits         9825     9825           
  Misses       3002     3002           

Files with missing lines	Coverage Δ
src/scanpy/plotting/_rcmod.py	100.00% <100.00%> (ø)

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[senseibence]

Could someone help with the checks for this PR?