Fix some type issues exposed via the API

[lossyrob]

These couple of issues were found while reviewing #561. VS Code running pylance/pyright showed some errors. This PR fixes errors that would be exposed to users using that tooling with PySTAC.

The first is straightforward, the setter of SummariesLabelExtension.label_properties was mis-typed.

The second is more subtle - for structural typing, it is required that the parameter names of the method in the Protocol be the same as the implementing type in order for type checking to pass. We defined a Comparable Protocol that required a method __lt__(self, x: T) -> bool, which was used as the bounds for the RangeSummary generic type. This works with things like floats and ints, which define their __lt__ methods with the parameter name being x. However, datetime.datetime defines it's method as __lt__(self, other). This caused Pyright to say that datetime didn't fit the structural type, and so RangeSummary[datetime] was not valid.

This PR moves splits Comparable protocol into two, _Comparable_x and _Comparable_other. I think the underscore naming here is appropriate I think as it's not for usage by PySTAC users but instead an internal mechanism. I then changed the bounds of the T TypeVar that's used in RangeSummary to be Union[_Comparable_x, _Comparable_other], which allows structural types that fit either the x or other parameter naming for the __lt__ method to pass the type linter.

This covers numeric types and datetime, but to note is that if a user wants to create a RangeSummary of a type that does support lt but names the parameter differently, Pyright will call that an error. I couldn't find a way to try and get the structural type to ignore the parameter name.

There were a few other errors that Pyright was reporting, but those were only for internal code, were particular to how pyright things about types, and so changes for those were not included.

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 #562 (d533785) into main (0ba1a1d) will decrease coverage by 0.00%.
The diff coverage is 85.71%.

@@            Coverage Diff             @@
##             main     #562      +/-   ##
==========================================
- Coverage   94.46%   94.45%   -0.01%     
==========================================
  Files          71       71              
  Lines       10728    10732       +4     
  Branches     1075     1075              
==========================================
+ Hits        10134    10137       +3     
- Misses        419      420       +1     
  Partials      175      175              

Impacted Files	Coverage Δ
pystac/summaries.py	76.68% <83.33%> (-0.05%)	⬇️
pystac/extensions/label.py	93.65% <100.00%> (ø)

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