Spatial tutorial

[mattjones315]

This PR implements the framework for a spatial library. Already, there were pieces of this library such as the ClonalSpatialDataSimulator; here, we implement a separate module - spatial - which currently implements a spatial imputation procedure.

We also include a tutorial notebook for the spatial data.

[codecov]

Codecov Report

❌ Patch coverage is 78.26087% with 20 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.91%. Comparing base (8bbcd10) to head (8b36987).
⚠️ Report is 25 commits behind head on master.

Files with missing lines	Patch %	Lines
cassiopeia/spatial/spatial_utilities.py	62.85%	13 Missing ⚠️
cassiopeia/preprocess/utilities.py	81.48%	5 Missing ⚠️
cassiopeia/spatial/spatial_imputation.py	91.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #262      +/-   ##
==========================================
- Coverage   79.77%   74.91%   -4.87%     
==========================================
  Files          91       94       +3     
  Lines        8347     8454     +107     
==========================================
- Hits         6659     6333     -326     
- Misses       1688     2121     +433     

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[colganwi]

Looks good @mattjones315! My major comment is that its not worth adding squidpy as a dependency just for the spatial_neighbors method. Users can precompute the neighborhood graph before running impute_spatial_data.