Replace pylint with more flake8 plugins

[leouieda]

Following fatiando/harmonica#285, replace pylint with a bunch of new flake8 plugins. They cover most of the checks that were performed before, add a few new ones, and are less troublesome to maintain and silence when necessary. Fixes the formatting issues raised after applying the changes: making tutorials/examples fit 79 char comments/docstrings, silence a few issues because of scikit-learn style code, reorder imports because of isort. I also combined the CI checks into only 2: "format" and "style". If formatting is broken, we don't need to know which one is complaining, just run make format. And style is now only flake8 anyway.

Reminders:

• Run make format and make check to make sure the code follows the style guide.
• Add tests for new features or tests that would have caught the bug that you're fixing.
• Add new public functions/methods/classes to doc/api/index.rst and the base __init__.py file for the package.
• Write detailed docstrings for all functions/classes/methods. It often helps to design better code if you write the docstrings first.
• If adding new functionality, add an example to the docstring, gallery, and/or tutorials.
• Add your full name, affiliation, and ORCID (optional) to the AUTHORS.md file (if you haven't already) in case you'd like to be listed as an author on the Zenodo archive of the next release.

[leouieda]

This PR depends on #336 being merged and should be rebased to main once that happens.

[leouieda]

@santisoler just FYI this does a few simplifications on top of what you've done in Harmonica. Mainly some CI stuff and putting all the configuration in pyproject.toml and setup.cfg instead of a bunch of individual tool files. This will be particularly handy in the future when we transition away from setup.py.