Update Python version compatibility to range 3.10-12

[hakonanes]

Description of the change

Remove explicit compatibility for Python 3.8 and 3.9 and add it for 3.12. Fixes #515.

Test suite on CI is updated to use 3.11 and 3.12, with one runner for 3.10 and minimal version dependencies.

Bump lowest Matplotlib from >= 3.5 to >= 3.6.1 (skip 3.6.0 as it throws a gazillion+1 MatplotlibDeprecationWarnings).

Other changes:

• Remove unnecessary UTF-8 encoding for all files
• Remember to update changelog
• Ensure 100% test coverage with all dependencies installed (mention this in test dev guide)
• Remove do_3d_projection() in our minimal Arrow3D class as it seems (!) to be unnecessary with Matplotlib >= 3.6.1 Turned out to still be necessary.
• Update Matplotlib tests following >= 3.6.1

Progress of the PR

• Docstrings for all functions
• 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.
• Contributor(s) are listed correctly in __credits__ in orix/__init__.py and in
  .zenodo.json.

[pc494]

Good stuff, happy for you to merge.

[hakonanes]

Thanks for the swift review!