Add pixi as an workflow/package manager

[ruben-arts]

This is an extension of the initial work I did live on the podcast we just recorded with Robin Beer.

We don't work with a single environment having multiple version of python. So I created a test environment per python version. (Ongoing brainstorming how to make this more comfortable)

Let me know what you think, would be glad to add more explanations or documentation in general.

ps. I'm not just pushing my own project, Robin asked me to 😉

[bbelderbos]

@ruben-arts cool, I will merge after watching you see do it on the podcast, thanks.

[bbelderbos]

Nice, thanks! Enjoyed the podcast, thanks for hopping on and sharing your work, some edits to still be made and then we'll publish it.