Add kerr evolution test mc

[ffoucart]

Proposed changes

Add a test for moving particles in the Kerr metric

Upgrade instructions

NA

Code review checklist

• [ ] The code is documented and the documentation renders correctly. Run make doc to generate the documentation locally into BUILD_DIR/docs/html. Then open index.html.
• [ ] The code follows the stylistic and code quality guidelines listed in the code review guide.
• [ ] The PR lists upgrade instructions and is labeled bugfix or new feature if appropriate.

[ffoucart]

Not for review yet; work in progress with @SamanthaRath