Linting and code style

[Sam Cunliffe]

Making this a full issue to track some stylistic refactoring.

• black can autoformat ✅
• ruff throws up ~500 style errors that it can't fix
  • decide whether or not to convert to CamelCaseClasses and snake_case_members
  • if not: configure ruff to ignore.

• mypy throwing around 12 errors which we probably do want to fix.