MAINT: Merge update_docs branch

[derb12]

Description

• Updated the documentation theme to pydata-sphinx-theme, which overall looks nicer.
• Added a CI job for running doctests, with the idea being that each baseline correction method should eventually have an example or two, showing basic usage and any noteworthy features, which are tested to ensure the code runs as expected. Alongside adding these examples, it would be nice to update most docstrings with details concerning what each algorithm actually does, similar to what the algorithms section of the docs currently do, rather than just stating their names...
  • As an initial endeavor, added examples and additional information to the docstrings for asls, iasls, airpls, and arpls.

Since updating most docstrings is going to be a rather disruptive change, it'd be easier to merge this branch into development now and gradually update each method's docstring alongside other work so that I don't have to go through a merge conflict nightmare later.

Type of Pull Request

• Bug Fix
• New Feature
• Miscellaneous Changes (refactor, code improvements, etc.)
• Documentation or Example Programs

Pull Request Checklist

• New code and/or documentation is valid for use with the BSD 3-clause license.
• New code is fully documented with docstrings that follow Numpy style, if applicable.
• New code follows PEP 8 standards as closely as possible, if applicable.
• Added/updated tests and ensured they pass locally, if applicable.
• Verified that documentation builds locally, if applicable.

[derb12]

Can ignore the failure on the nightly job, that's from my own deprecations that I can address after merging.