Use Ruff and enforce full type annotation coverage

[JelleZijlstra]

I got here because I was trying to get rid of some no-untyped-call mypy errors internally, which were because our __init__ method doesn't have annotations. To fix it thoroughly:

• Use Ruff to enforce full annotation coverage
• Also replace other linting tools (pyupgrade, pycln, isort, flake8) so we have fewer tools to worry about
• Update the project URL because I noticed it
• Fix any new errors