Experimental Python 3.10 support

[duckontheweb]

Related Issue(s):

• Bring code coverage back up to 93-94% #331

Description:

Adds Python 3.10 to the test matrix, but allows the CI workflow to succeed even if any Python 3.10 job fails. The main hiccup is that orjson does not have Python 3.10 wheels for Windows or MacOS, and needs the Rust nightly toolchain to build. The CI job installs Rust nightly for Python 3.10 jobs, and this PR adds a note in the Installation docs describing this requirements.

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 #473 (40f16a5) into main (13a9fad) will increase coverage by 0.17%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #473      +/-   ##
==========================================
+ Coverage   91.48%   91.66%   +0.17%     
==========================================
  Files          40       40              
  Lines        5240     5245       +5     
==========================================
+ Hits         4794     4808      +14     
+ Misses        446      437       -9     

Impacted Files	Coverage Δ
pystac/__init__.py	100.00% <0.00%> (ø)
pystac/errors.py	90.00% <0.00%> (+1.11%)	⬆️
pystac/stac_io.py	82.75% <0.00%> (+5.56%)	⬆️

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[duckontheweb]

cc: @l0b0