feat: _potential_energy with Quantity

[nstarman]

Quantities in most places.

[codecov]

Codecov Report

Attention: Patch coverage is 93.47826% with 9 lines in your changes are missing coverage. Please review.

Project coverage is 89.46%. Comparing base (c972652) to head (2cf0796).
Report is 73 commits behind head on main.

Files	Patch %	Lines
src/galax/potential/_potential/base.py	88.88%	6 Missing ⚠️
src/galax/potential/_potential/io/gala.py	0.00%	1 Missing ⚠️
src/galax/potential/_potential/param/field.py	87.50%	1 Missing ⚠️
src/galax/potential/_potential/utils.py	96.29%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #187      +/-   ##
==========================================
+ Coverage   88.44%   89.46%   +1.02%     
==========================================
  Files          42       53      +11     
  Lines        1324     1813     +489     
==========================================
+ Hits         1171     1622     +451     
- Misses        153      191      +38     

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