• Add pixi to run codegen in a portable way #3707 seems very compelling

Pixi should be able to replace all of our current just commands while bringing the added benefit of running things in an environment with managed dependencies. For example, this gives us access to our code-gen dependencies, the arrow-cpp we need for building rerun-cpp, etc.

This lets us replace all of the commands in just with versions that handle the dep installation first.
This also lets us collapse many of the layers of our Dockerfile into a single pixi install invocation.

TODO

• Use pixi on CI
  • C++: Reopen Use pixi for all cpp test invocations on CI #3921
• Replace venv with pixi
• Replace the alias section in .cargo/config.toml with just commands wrapping pixi #4171
• Replace scripts/requirements-dev.txt etc
• Replace our setup*.sh files with pixi #4170
• Replace our other .sh scripts, if possible (https://prefix.dev/docs/pixi/advanced/advanced_tasks)
• Publish rerun on pixi
• …