Chromatic noise updates

[jeremy-baier]

This PR contains many various updates associated with chromatic noise modeling efforts over the past several years. Notable changes include:

• functionality for “fixed-point” analysis where one can set a chromatic signal to a max likelihood value rather than sampling in that GPs hyperparameters.
• the ability to sample in the chromatic index of a chromatic model.
• it also expands functionality for empirical distributions to include a hypermodel empirical distribution.
• cleans up the hypermodel code caching stuff which is called in each iteration unnecessarily
• move the hypermodel weights to the lnPRIOR rather than the lnLIKELIHOOD (fixes issues with PTMCMC and hm weights)
• prints hypermodel weights to a file in out directory (model_log_weights.json)

[jeremy-baier]

tagging @Hazboun6 and @blarsen10 since Jeff coded most of these changes originally. trying to put together a to-do list here for the PR:

• [ ] clean up comments
• [x] linting
• [ ] write a test for empirical distribution hypermodel
• [x] write a test for the chromatic model?
• [x] make the upper bound on the gp idx prior variable?

[Hazboun6]

@AaronDJohnson do you recognize the errors that are happening in the mac installs? It's a libstempo issue, so it doesn't even get to the actual unit tests.

[blarsen10]

This also now adds support for the SW GP basis & kernel from Nitu et al 2024

[Hazboun6]

@blarsen10 and @jeremy-baier Can we have a look at the errors here ASAP. From what I saw it's just not passing the linting rules. It would be good to get this merged this week.