Test pixi package manager

[jorisv]

Test pixi package manager to ease CI steps and help new developers. Also, fix cache use for ccache.,

• [x] Create pixi.toml
• [x] Test CI
• [x] Test conda recipe build
• [x] Check ccache cache
• [x] Update README.md

Pro:

• Lock file make CI build faster
• prefix-dev/setup-pixi cache make CI build faster
• Dependencies are well documented
• New developer can easily build the project
• Pixi is connected to the CI and must be maintained
• No need to install anaconde (pixi package it)

Con:

• New tool to install and learn

[ManifoldFR]

What are we doing with this ? Since we've got it on eigenpy now

[jorisv]

It's still not merged on eigenpy.

I have a last check to do: is it convenient to work with multiple source project and pixi ?

[ManifoldFR]

Is this still supposed to be opened after #113 was merged ?

[jorisv]

Oh boy, I forget this one ! We can close it :)