add pixi env management

[corednoir]

this pr adds a functional (from my tests) cpu-only using pixi as package management.

it also adds a placeholder for others with gpu-acess to implement.

its easier to control, and project oriented (https://pixi.prefix.dev/dev/#quick-demo)

one would only need to run, for example:

pixi install -e cpu/gpu
pixi run --as-is app