Use Nix to provide multiple CI tests.

**Type of issue**: feature request

**Impact**: no functional change

**Development Phase**: proposal

yesterday, I changed CI of my own project to Nix in https://github.com/sequencer/arithemic/blob/5384c09f9c229fa5a1ec265077c74aecff2ff420/.github/workflows/push.yml, which provides a neat way to lock version and download compiled caches.
I think we can try this in Chisel upstream repository:
firstly add test matrixes after pushing to master, if it run well
we can switch to Nix to provides a neat CI infrastructure, rather than depending on a specific distro.