Preserve integer types

[dbaston]

Update core classes so that integer raster types are handled throughout, rather than coercing everything to a double.

[codecov]

Codecov Report

Attention: 20 lines in your changes are missing coverage. Please review.

Comparison is base (1ce4c39) 51.00% compared to head (ea5bbc1) 51.40%.

Files	Patch %	Lines
src/feature.cpp	57.14%	6 Missing ⚠️
src/operation.cpp	91.80%	5 Missing ⚠️
src/gdal_feature.h	0.00%	3 Missing ⚠️
src/raster_sequential_processor.cpp	62.50%	3 Missing ⚠️
src/raster_coverage_iterator.h	33.33%	2 Missing ⚠️
src/coverage_operation.h	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #57      +/-   ##
==========================================
+ Coverage   51.00%   51.40%   +0.40%     
==========================================
  Files          72       72              
  Lines       11694    11770      +76     
==========================================
+ Hits         5964     6050      +86     
+ Misses       5730     5720      -10     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.