Set up docs/CI in repo

See Anish's recommendations (from `#tlm` Slack channel):

- Project manager and [build backend](https://packaging.python.org/en/latest/guides/tool-recommendations/#build-backends): [Hatch](https://hatch.pypa.io/) and Hatchling
- I see you're already using this
- Installer: [uv](https://docs.astral.sh/uv/) (via installer = "uv" option in pyproject.toml)
- Lot faster than the default pip installer
- For a Python library using Hatchling as the build system, I don't think you need the .python-version or uv.lock
- Code quality and CI: GitHub Actions, Mypy, Ruff (via hatch fmt), Pytest (via hatch test), [Codecov](https://app.codecov.io/)
- We use (subsets of) these in our existing projects like [airline-agent](https://github.com/cleanlab/airline-agent) and [cleanlab](https://github.com/cleanlab/cleanlab)
- Docs: [mkdocs-material](https://squidfunk.github.io/mkdocs-material/) and [mkdocstrings-python](https://mkdocstrings.github.io/python/), built in GitHub Actions and hosted using GitHub pages ([via artifact](https://github.com/actions/upload-pages-artifact), not branch)
- Popular libraries like [Pydantic AI](https://github.com/pydantic/pydantic-ai) and [DSPy](https://github.com/stanfordnlp/dspy) use mkdocs-material, you could take inspiration from their configuration. I also used this documentation system for a [personal project](https://github.com/anishathalye/semlib) a couple months ago, feel free to copy configurations from there.