Add nix build to CI

[seam345]

It builds \o/

Naming

I'm not so well versed with github workflow, but I think I had to give this build a different name due to it being a totally different set of commands
happy to rename "nix-tests" to anything else

UI Tests missing

As I just copied over the nixpkgs version I have missed off the cargo ui-testI will add this before marking this as not a draft

Trade offs

I built it with basically the identical package.nix in the nixpkgs i made

• pro
  • Any change to this is easily converted to the nixpkgs build, so helps me keep them in sync till we get it into nixpkgs
• con
  • building requires this weird invocation -E 'with import <nixpkgs> { }; callPackage ./default.nix {}'
  • I think built with flakes or not in a nixpkgs way would allow people to just nix-build or nix build and point at the mutest-rs repo
    • I might try investigate this before marking as not draft

[seam345]

oh here's the CI build https://github.com/seam345/mutest-rs/actions/runs/29189979551/job/86642818328 I should work out if can colourise the cargo output in nix as well