Make builtin potential list alphabetical (and simplify public API export??)

[adrn]

This first sorts the list of potential names alphabetically in the builtin __init__.py. I then also was puzzling at why we need another manual list of potential names in galax/potential/__init__.py for the public API -- it's annoying to have to maintain the list of names in so many places! Can we just dynamically add to __all__ like this, since anything exported at the builtin/__init__.py level should probably be public API anyway?

[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 95.84%. Comparing base (ef83e69) to head (3f5a10b). :warning: Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #757   +/-   ##
=======================================
  Coverage   95.84%   95.84%           
=======================================
  Files         158      158           
  Lines        5963     5965    +2     
=======================================
+ Hits         5715     5717    +2     
  Misses        248      248           

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

:rocket: New features to boost your workflow:

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

[nstarman]

I like the idea of simplifying the __init__.py. But I think the public-facing one should have the statically defined list. This can be important for tools.