Tidy up local dev and codebase

[pm5k]

Proposal

• Enact a code freeze and notify all devs that no dev is to take place between 23rd Dec and 2nd Jan

In separate PRs:

• Move project to Poetry and Python 3.11
• Apply isort / black / flake8 fixes
• Add mkdocs/mkdocstrings and use github actions to build a public github pages app to host the docs
• Consider applying Typer as the new CLI handler for the project
• Review some of the current code for various tidy actions like typing, DRYness and other basic stuff

Acceptance criteria

• New state of codebase is cleaner, easier to maintain and document, better to understand, uses more modern tooling