Move Python configuration to pyproject.toml

[jwhitlock]

Make several changes to centralize Python configuration in pyproject.toml:

• Set the minimum Python version to 3.11, which allows black to use parenthesized context managers from Python 3.10.
• Move config for paul-mclendahand from setup.cfg to pyproject.toml
• Move config for pytest from pytest.ini to pyproject.toml
• Alphabetize pyproject.toml where appropriate

[jwhitlock]

This is all non-production code (configuration and tests), so I'm skipping review.