chore(ci): add nix flake build

[ch4og]

Description of change

Adds flake building to CI

Help is needed to add rust-cache support

[ch4og]

AFAIK pkgs.rustPlatform.buildRustPackage can't use rust-cache so I have no idea what can be done

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 3.33%. Comparing base (4bc6b7a) to head (b998cde). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #75 +/- ## ===================================== Coverage 3.33% 3.33% ===================================== Files 19 19 Lines 2407 2407 ===================================== Hits 80 80 Misses 2327 2327 ```

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[orhun]

Maybe @jla2000 or @Titaniumtown has an idea about this

[jla2000]

@ch4og I think you will need to cache the nix store.

[Titaniumtown]

Maybe @jla2000 or @Titaniumtown has an idea about this

I'm not too familiar with using nix with github actions, srry :(

[ch4og]

@ch4og I think you will need to cache the nix store.

Doesn't nix magic cache do this?

[ch4og]

Should be good to merge

Caching nix store using other way worked. It uses cache after first build now

But this build time can be decreased even more with https://github.com/orhun/binsider/pull/76