feat: multipole potentials

[nstarman]

Multipole potentials. Inner, Outer, & Combined.

This currently does not support time dependence on S/Tlm, but that's entirely because of the __check_init__.

[codecov]

Codecov Report

Attention: Patch coverage is 88.27586% with 17 lines in your changes missing coverage. Please review.

Project coverage is 89.96%. Comparing base (5a01695) to head (54d9d60).

Files	Patch %	Lines
src/galax/_galax_interop_gala/potential.py	0.00%	17 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #357      +/-   ##
==========================================
- Coverage   94.68%   89.96%   -4.72%     
==========================================
  Files          70       71       +1     
  Lines        2500     2642     +142     
==========================================
+ Hits         2367     2377      +10     
- Misses        133      265     +132     

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[nstarman]

Given that there's no combined inner/outer multipole expansion in Gala, this wasn't being tested by the automatic testing framework. I'll write a specific test.

[nstarman]

@adrn, I think there are more efficient ways to compute this, but this implementation is already quite performant both during and post JIT. I think further efficiencies and code consolidation can happen in a followup PR.
Also, I'm very interested (in a followup PR) to implement sparsity support for S/T_lm!

[nstarman]

That's a strange one. It was passing. Shouldn't be failing now!
Also, it passes on my laptop.