Switch doc theme from Furo to PyData

[hakonanes]

Description of the change

This PR switches the doc theme from Furo to PyData. While I find Furo more pleasing, I find navigating the API reference more challenging. Having read API references in other packages (Matplotlib, SciPy, PyVista) using the PyData theme, and finding it easier to navigate, I suggest we use the same theme.

The PyData theme has narrower content, so I had to format the tutorial notebooks with a 80 character line length. Since the code allows 88 characters, and this is what Black checks for (can only configure this for both scripts/notebooks, not separately), I removed the notebook check in the pre commit config. The PR check is updated accordingly. Contributors will have to format notebooks themselves, which is mentioned in the contributing guide.

I anticipate this to be the final change before releasing v0.7.0.

Progress of the PR

• [n/a] Docstrings for all functions
• [n/a] Unit tests with pytest for all lines
• Clean code style by running black via pre-commit

For reviewers

• The PR title is short, concise, and will make sense 1 year later.
• New functions are imported in corresponding __init__.py.
• New features, API changes, and deprecations are mentioned in the unreleased
  section in CHANGELOG.rst.
• New contributors are added to release.py and .all-contributorsrc and the table
  is regenerated.