As a frontend to Ruff's formatter.
There are some interesting choices here, some of which may just be
temporary:
1. We pin a default version of Ruff, so `uv format` is stable for a
given uv version
2. We install Ruff from GitHub instead of PyPI, which means we don't
need a Python interpreter or environment
3. We do not read the Ruff version from the dependency tree
See https://github.com/astral-sh/ruff/pull/19665 for a prototype of the
LSP integration.
