Sphinx 9 compatibility

[mkelley]

Why did this become a problem now? 🤷🏻 But LinearPhaseFunc's empty defaults causes the documentation build to crash with the latest Sphinx.

While I'm here, I'll also add some doc substitutions used in astropy for (a) consistency, and (b) so that sbpy's ArbitraryFrame can inherit astropy docstrings.

[github-actions]

Thank you for your contribution to sbpy, an Astropy affiliated package! 🌌 This checklist is meant to remind the package maintainers who will review this pull request of some common things to look for.

• Do the proposed changes actually accomplish desired goals?
• Do the proposed changes follow the sbpy coding guidelines?
• Are tests added/updated as required? If so, do they follow the Astropy testing guidelines?
• Are docs added/updated as required? If so, do they follow the Astropy documentation guidelines?
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[mkelley]

@hhsieh00 Can you review / approve ignoring the MacOS failure? I will address this in #427

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.72%. Comparing base (843b1a2) to head (cc363b7).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #433   +/-   ##
=======================================
  Coverage   84.72%   84.72%           
=======================================
  Files          92       92           
  Lines        8459     8459           
=======================================
  Hits         7167     7167           
  Misses       1292     1292           

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[hhsieh00]

Looks good to me