[Doc]: Consider switching documentation theme to `pydata-sphinx` like `xarray`

[tomvothecoder]

Describe your documentation update

Xarray switched over from sphinx-book-theme to pydata-sphinx. This new theme utilizes a top-level primary navigation bar, while the primary sidebar on the left now contains sub-pages. This makes the documentation less cluttered and easier to navigate.

Example: https://docs.xarray.dev/en/stable/

Related to:

• https://github.com/pydata/xarray/pull/8708