properties -> extra_fields for Asset and Link

[duckontheweb]

Related Issue(s):

• Support for 'processing' extension in pystac.Provider #479 (see this comment)
• Create type annotations for attributes  #321

Description:

Adds type annotations for Link and Asset attributes and uses these in API documentation. Changes properties to extra_fields for Link and Asset classes to use more consistent naming across PySTAC classes.

PR Checklist:

• Code is formatted (run pre-commit run --all-files)
• Tests pass (run scripts/test)
• Documentation has been updated to reflect changes, if applicable
• This PR maintains or improves overall codebase code coverage.
• Changes are added to the CHANGELOG. See the docs for information about adding to the changelog.

[codecov-commenter]

Codecov Report

Merging #510 (4b4bc51) into main (a4fe4cd) will increase coverage by 0.00%.
The diff coverage is 97.50%.

@@           Coverage Diff           @@
##             main     #510   +/-   ##
=======================================
  Coverage   93.96%   93.97%           
=======================================
  Files          71       71           
  Lines        9991    10000    +9     
  Branches     1061     1059    -2     
=======================================
+ Hits         9388     9397    +9     
  Misses        434      434           
  Partials      169      169           

Impacted Files	Coverage Δ
pystac/extensions/item_assets.py	65.85% <ø> (ø)
tests/extensions/test_custom.py	54.83% <0.00%> (ø)
pystac/item.py	93.16% <97.29%> (ø)
pystac/asset.py	87.71% <100.00%> (+0.92%)	⬆️
pystac/extensions/datacube.py	62.26% <100.00%> (ø)
pystac/extensions/eo.py	94.33% <100.00%> (ø)
pystac/extensions/file.py	92.30% <100.00%> (ø)
pystac/extensions/label.py	93.55% <100.00%> (ø)
pystac/extensions/pointcloud.py	95.04% <100.00%> (ø)
pystac/extensions/projection.py	97.60% <100.00%> (ø)
... and 11 more

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[gadomski]

LGTM. The only thing that was initially surprising was the properties attribute on all extensions, but it made sense after reading for a bit (they aren't extra fields, they really are the extension's data).

[duckontheweb]

LGTM. The only thing that was initially surprising was the properties attribute on all extensions, but it made sense after reading for a bit (they aren't extra fields, they really are the extension's data).

Yeah, I thought that was too much to take on in this PR, but I agree that is confusing terminology as well. It also interferes with the naming convention in the Label Extension, since that defines a "label: properties" attribute. I can open a separate issue to discuss whether we want to change that.