docs: add pixi environment

[esadek]

Add a docs environment, dependencies, and tasks to the Pixi manifest. With Pixi, there’s no need to manually create and activate a Python virtual environment or install mkdocs and cairo.

[amoeba]

Thanks. Added one question as a comment above.

I think we might also consider updating everywhere we're using venvs to just use the new pixi setup (docs/ folder, CI). What do you think?

[esadek]

I think we might also consider updating everywhere we're using venvs to just use the new pixi setup (docs/ folder, CI). What do you think?

I agree. Would you like that included in this PR?

[amoeba]

Either way. Doing it in a follow-up is fine too.

[esadek]

I've updated docs/README.md and .github/workflows/publish_docs.yml to use Pixi.

[amoeba]

Nice, one change.

I like this (using pixi) even more now that I realize we can remove the extra setup defined in https://squidfunk.github.io/mkdocs-material/plugins/requirements/image-processing/#cairo-graphics-macos.

[esadek]

Yes, having Cairo automatically installed into the environment is awesome.