Fix some documentation issues

[speth]

Changes proposed in this pull request

• Pin sphinx and pydata theme versions for 3.1 release
• Add missing argument lists to class declarations in reST files. Add notes about this requirement to the developer documentation.
• Add missing classes to the Python reference docs
• Add a SCons option to skip running the examples (which can take a long time and is annoying when you're just trying to fix parts of the API docs).

If applicable, fill in the issue number this pull request is fixing

• Fixes Sphinx search results show "404: Page not found" in preview snippets #1692
• Fixes Sphinx doesn't show constructor arguments for some classes #1635

If applicable, provide an example illustrating new features this pull request is introducing

Checklist

• The pull request includes a clear description of this code change
• Commit messages have short titles and reference relevant issues
• Build passes (scons build & scons test) and unit tests address code coverage
• Style & formatting of contributed code follows contributing guidelines
• The pull request is ready for review

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.69%. Comparing base (1ed2b28) to head (7024f6b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1702   +/-   ##
=======================================
  Coverage   75.69%   75.69%           
=======================================
  Files         443      443           
  Lines       60971    60971           
  Branches     9552     9552           
=======================================
  Hits        46154    46154           
  Misses      11786    11786           
  Partials     3031     3031           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.