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
• linting
• write a test for empirical distribution hypermodel
• write a test for the chromatic model?
• 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.

[Hazboun6]

@jeremy-baier and @blarsen10 I think that the reason the tests are still failing is that GitHub CI uses the setup.py to setup the environment for the tests. That doesn't limit the scipy version yet.

[AaronDJohnson]

@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.

Sorry for the delay on all of this. Feel free to ping me again if you don't get a reply quickly next time! I did know exactly what was happening, and I've merged a fix. If @jeremy-baier pulls from upstream/main, the Mac tests should be fixed now. The new runners only support ARM architectures, so we have to go back one version on the CI runners so that they run an x86 architecture instead.

[AaronDJohnson]

I've also fixed the scipy issue by updating to the new recommended function. So you can remove the maximum version number on scipy here.