Check formatting, lint, and typecheck in CI

[gjoseph92]

Format with shed.
Lint in CI with flake8.
Typecheck in CI with pyright (way faster, seems to get new features sooner than mypy, and built into vscode).

Consider also adding pre-commit hooks (and https://pre-commit.ci) for all these things. I somewhat dislike the slowdown of pre-commit hooks, but overall they are nicer than CI failures!