Pre-release fixes and improvements

[AdeelH]

Overview

This PR makes some minor fixes and improvements, adds/updates unit tests and docs, and does some refactoring.

Eval changes

Checklist

• Added needs-backport label if PR is bug fix that applies to previous minor release
• Ran scripts/format_code and committed any changes
• Documentation updated if needed
• PR has a name that won't get you publicly shamed for vagueness

Notes

N/A

Testing Instructions

• See new unit tests.

[codecov]

Codecov Report

Merging #1857 (5121058) into master (ee3fbef) will increase coverage by 0.81%.
The diff coverage is 91.61%.

@@            Coverage Diff             @@
##           master    #1857      +/-   ##
==========================================
+ Coverage   80.79%   81.61%   +0.81%     
==========================================
  Files         188      190       +2     
  Lines        9260     9278      +18     
==========================================
+ Hits         7482     7572      +90     
+ Misses       1778     1706      -72     

Files Changed	Coverage Δ
.../data/raster_transformer/nan_transformer_config.py	100.00% <ø> (+25.00%)	⬆️
...ner/rastervision/pytorch_learner/learner_config.py	83.09% <ø> (-0.06%)	⬇️
...sion_core/rastervision/core/data/utils/rasterio.py	86.73% <86.73%> (ø)
...vision_core/rastervision/core/data/utils/raster.py	97.05% <97.05%> (ø)
rastervision_core/rastervision/core/box.py	100.00% <100.00%> (ø)
...sion/core/data/label/chip_classification_labels.py	100.00% <100.00%> (+12.34%)	⬆️
...rvision/core/data/label/object_detection_labels.py	97.12% <100.00%> (+2.15%)	⬆️
...on/core/data/label/semantic_segmentation_labels.py	91.53% <100.00%> (ø)
...label_source/semantic_segmentation_label_source.py	93.87% <100.00%> (-0.57%)	⬇️
...a/label_store/semantic_segmentation_label_store.py	92.52% <100.00%> (+0.34%)	⬆️
... and 6 more

... and 42 files with indirect coverage changes