switch to pixi

[aryarm]

Once poetry 2.0 is released (hopefully this month?), we could consider switching from conda to pixi!

The benefit of this is that we will be able to move the contents of our dev-env.yml file config into our pyproject.toml file like this. This will also allow us to lock our conda dependencies in a pixi.lock file

The release of poetry 2.0 will make it so that we won't need to duplicate our dependency list as described here

On the user-facing side, everything will be pretty much the same. But on the development side, we will need to adapt our devcontainer.json and GitHub actions to use pixi instead of conda