WIP: feat time domain solar wind covariance

[jeremy-baier]

Needed for NG20.
Major changes

• Making phi either 1d or 2d. Necessary for 2-dimensional kernels.
• Addition of said 2d kernels for the solar wind only for now.
• Time domain interpolation bases to go with the above. Both custom ( for Bayesian Blocking ) and uniform bins.
• Since above, need to switch trivia phi inversion to use a cholesky decomposition with a np inversion fallback.

More work should really explore additional caching of various parts of the GLS fit when the noise model is being held constant. This might be sub blocks of the design matrix. Or a refactorization of the GLS implementation.

TODO

• unit tests
• should check that our basis and phi matrix match those of discovery. (might consider adding tests for this).
• additional model validations ?

Disclosure that I used co-pilot for generating the unit tests as well as some docstrings and type hinting.