ENH: support pixi and venv in .envrc

[redeboer]

Follow-up to #354, now with support for venv, uv venv, and pixi environments.

[shenvitor]

Impressive update!

[redeboer]

Fancy and handy, but it is not necessarily good practice. A repo with it's own .envrc makes it almost impossible to work with your own custom .envrc. It can also pose a security risk if you just run direnv allow on some cloned repo that provides its own .envrc, see e.g. this discussion.

Anyway, for now I see it as a bridge towards #333, especially with uv and/or pixi.