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 #1692
• Fixes #1635

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

Checklist

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

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

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

Additional details and impacted files

```diff @@ 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 ```

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