Export geoagents and raster cells

[wang-boyu]

• Extract raster cells as numpy array and save to file. Addresses Convenient methods in RasterLayer #91 (comment).
• Extract geoagents as geodataframe.
• Update rainfall and geo_schelling examples to demonstrate.

[codecov]

Codecov Report

Merging #98 (38abc49) into main (c54624c) will increase coverage by 0.62%.
The diff coverage is 90.00%.

@@            Coverage Diff             @@
##             main      #98      +/-   ##
==========================================
+ Coverage   79.28%   79.90%   +0.62%     
==========================================
  Files           7        7              
  Lines         584      622      +38     
  Branches       98      108      +10     
==========================================
+ Hits          463      497      +34     
- Misses        105      108       +3     
- Partials       16       17       +1     

Impacted Files	Coverage Δ
mesa_geo/raster_layers.py	73.92% <88.88%> (+1.51%)	⬆️
mesa_geo/geospace.py	85.39% <92.30%> (+0.54%)	⬆️

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.