Use ruff for linting #87
Description
We currently use flake8 for linting, but ruff provides a nice way to consolidate linting rules used/defined by various other tools, such as black and flake8. We should also remove the "special" linting cases currently run only as part of CI (see .github/workflows/python-app.yml). Linting should be applied the same way, whether we're contributing code or running CI.