Add classification extension

[jpolchlo]

Related Issue(s):
Closes #788

Description:
This PR adds the Classification Extension to pystac.

PR Checklist:

• pre-commit hooks pass locally
• 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.

[jsignell]

In case it's helpful I have some pytest-style extension tests in #1088

[codecov-commenter]

Codecov Report

Patch coverage: 95.61% and project coverage change: +0.39 🎉

Comparison is base (37dcf01) 90.52% compared to head (b07864b) 90.91%.

❗ Current head b07864b differs from pull request most recent head 9e7a1a7. Consider uploading reports for the commit 9e7a1a7 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1093      +/-   ##
==========================================
+ Coverage   90.52%   90.91%   +0.39%     
==========================================
  Files          48       49       +1     
  Lines        6355     6606     +251     
  Branches      944      970      +26     
==========================================
+ Hits         5753     6006     +253     
+ Misses        426      421       -5     
- Partials      176      179       +3     

Impacted Files	Coverage Δ
pystac/extensions/classification.py	95.60% <95.60%> (ø)
pystac/__init__.py	94.54% <100.00%> (+0.10%)	⬆️

... and 2 files with indirect coverage changes

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[jpolchlo]

@jsignell I modeled my tests after the EO extension tests, are we saying that the pytest style is now preferred?

[jsignell]

@jsignell I modeled my tests after the EO extension tests, are we saying that the pytest style is now preferred?

Yeah the plan is to move all the tests to pytest eventually #993

[jpolchlo]

@gadomski You can flick your eyes over this. Tests need to get revamped, but the interface seems fine now.

[gadomski]

Can you add a test to ensure we can open an object that has the older classification version, ala https://github.com/stac-utils/pystac/pull/1131/files#diff-89b2d9c743703076080598ace41425b7270c1c0dc767f431ff7cab1c2b396b70R428-R443

[gadomski]

@jpolchlo sorry, I'm not seeing the test to ensure we can read v1.0.0...am I missing it?

[jpolchlo]

@gadomski All of the examples in tests/data-files/classification use the 1.0.0 version. I'll update one to use 1.1.0 as well to be sure our bases are covered?

[gadomski]

@gadomski All of the examples in tests/data-files/classification use the 1.0.0 version. I'll update one to use 1.1.0 as well to be sure our bases are covered?

Ah gotcha. Yeah, whatever version the test files are in, I'd like to make an explicit test that the other version works too (aka you can access the extension object and its properties). Thanks.

[jpolchlo]

Are you proposing that each test be run twice for each version of the extension? Given how these extensions work, it feels like it should be enough to simply show that the different versions can be read by the extension, since all the functionality is otherwise identical. The code coverage report is showing that nearly all of the code pathways are exercised by the tests provided, and because in this case the 1.1.0 version is a superset of the 1.0.0 version, it feels like the work done here should be sound. Let me know if that's incorrect.

[gadomski]

Are you proposing that each test be run twice for each version of the extension?

No, just a single test to ensure that we can read the version not in the fixtures, e.g. https://github.com/stac-utils/pystac/pull/1131/files#diff-89b2d9c743703076080598ace41425b7270c1c0dc767f431ff7cab1c2b396b70R428-R443

Need one more test to ensure we can handle both versions