Add automation for lint, format, and type check

[zanieb]

Follows #236 (comment)

Adds a check.py script and splits some requirements into requirements.dev.in / .txt. Enforces checks in a CI job.

Runs:

• ruff check with a very limited selection of rules, can add more later
• ruff format
• mypy on a subset of modules

A --fix flag can be provided to apply linter fixes and reformat files.

[indygreg]

This was long overdue. Thank you for doing this!