Describe your changes

This addresses an ancient feature self-request in #39, to add a shorthand for calling potential methods (e.g., .circular_velocity) when a potential has a coordinate symmetry.

Unit tests were generated with Claude 😬.

Checklist

• Did you add tests?
• Did you add documentation for your changes?
• Did you reference any relevant issues?
• Did you add a changelog entry? (see CHANGES.rst)
• Are the CI tests passing?
• Is the milestone set?

Fixes #39