Update sphinx multimethod customization to handle toplevel functions

[lorenzncode]

Fixes #1921

[lorenzncode]

solid example

current docs: https://cadquery.readthedocs.io/en/latest/classreference.html#cadquery.occ_impl.shapes.solid

PR: https://cadquery--1932.org.readthedocs.build/en/1932/classreference.html#cadquery.occ_impl.shapes.solid

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.84%. Comparing base (2e05819) to head (e2a7157).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1932   +/-   ##
=======================================
  Coverage   95.84%   95.84%           
=======================================
  Files          29       29           
  Lines        7922     7922           
  Branches     1191     1191           
=======================================
  Hits         7593     7593           
  Misses        192      192           
  Partials      137      137           

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

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[adam-urbanczyk]

Shall we merge this PR @lorenzncode ?

[lorenzncode]

@adam-urbanczyk The only other change I had planned was to pin the sphinx_rtd_theme to 3.1.0 when it is released.

Another idea was to move this sphinx customization out of the main cadquery repo say to CadQuery/sphinx-multimethod. The customization uses sphinx internals and will likely require changes with future updates to sphinx. I don't expect there to be very frequent maintenance of the customization however and I hope the docs remain stable pinned to sphinx 9.0.4 for some time.

Do you have any preference on keeping the customization with the docs or moving it to a separate repo?