Refactor algebraic circle fit routine

[samantha-ho]

This PR refactors the core algebraic circle fit routine for improved usability and readability.

The core algebraic circle fit has been pulled into a separate, stand-alone module for easier reuse outside this set of tools.

Additionally, the previously hardcoded equations for the coefficients of the characteristic polynomial of (M - xB) have been replaced by first converting to the related eigenvalue problem (MB_inverse - xI)B whose determinant is det(MB_inverse-xI)*det(B). This allows us to use the Faddeev-LeVerrier Algorithm to calculate the coefficients of the characteristic polynomial without needing to hardcode them, and improves the readability of the code.

Finally, the automatic code-formatting tool black was run on circlefit.py, causing numerous formatting changes.

[sebastianprobst]

Thank you for your contribution. I have 2 questions:

1. Can you confirm that the changed code produces identical results?
2. Does the code run slower now? By how much?