use uv

[davidism]

Use uv to manage dev dependencies.

• tox-uv sets up envs with uv and dependency groups
• pre-commit-uv sets up envs with uv
• workflows use uv to install dependencies, but still use setup-python to install python itself, since that's already cached by github.
• use uv to build during publish workflow
• read the docs uses a custom build step
• tox config is moved into pyproject.toml
• use new license metadata
• add a tox r -e docs-auto to start a local server that rebuilds on docs changes

New env setup steps are:

1. install uv
2. uv sync
3. uv tox (or activate venv as before)