Allow ChipClassificationLabelSource to load scores, if available, when reading labels

[AdeelH]

Overview

This PR Allow ChipClassificationLabelSource to load scores if available when reading labels from a vector source.

Checklist

• Added unit tests, if applicable
• Updated documentation, if applicable
• Added needs-backport label if the change should be back-ported to the previous release
• PR has a name that won't get you publicly shamed for vagueness

Notes

N/A

Testing Instructions

Covered by existing unit tests.

[codecov]

Codecov Report

Merging #1988 (297f833) into master (cd102da) will increase coverage by 0.01%.
Report is 8 commits behind head on master.
The diff coverage is 68.75%.

@@            Coverage Diff             @@
##           master    #1988      +/-   ##
==========================================
+ Coverage   86.14%   86.16%   +0.01%     
==========================================
  Files         195      195              
  Lines        9581     9598      +17     
==========================================
+ Hits         8254     8270      +16     
- Misses       1327     1328       +1     

Files	Coverage Δ
...s_sagemaker/rastervision/aws_sagemaker/__init__.py	100.00% <ø> (ø)
...vision_core/rastervision/core/analyzer/analyzer.py	100.00% <ø> (ø)
...ervision_core/rastervision/core/backend/backend.py	100.00% <ø> (ø)
...ision/core/data/crs_transformer/crs_transformer.py	100.00% <ø> (ø)
...vision_core/rastervision/core/data/label/labels.py	100.00% <ø> (ø)
...on/core/data/label/semantic_segmentation_labels.py	91.53% <ø> (ø)
...a/label_source/chip_classification_label_source.py	93.68% <100.00%> (+0.20%)	⬆️
...astervision/core/data/label_source/label_source.py	78.57% <100.00%> (+3.57%)	⬆️
.../rastervision/core/data/label_store/label_store.py	100.00% <100.00%> (ø)
...a/label_store/semantic_segmentation_label_store.py	94.41% <100.00%> (ø)
... and 17 more