Add explicit support for Python 3.12

[korverdev]

I'm planning on taking a look at this this weekend if nobody gets to this before me. Python 3.12 was officially released October 2nd.

• Confirm Codespell works using Python 3.12 and no deprecation warnings are being raised.
• Add Python 3.12 to CI testing.
• Update dev container to use Python 3.12.
• Update pyproject.toml.