Added nix check and pre commit hook for formatting

[Alexnortung]

After making my first commits to this project in a while I was met with an angry CI that didn't like I did not run nix fmt before committing/pushing. So I thought a good idea would be to provide a pre-commit hook, so I and others don't forget to format before committing.

Thanks to cachix/pre-commit-hooks.nix this was quite easy to implement.

To install the pre commit hooks simply open the devShell in the repository (nix develop). Or if you have direnv it will load automatically.

This was also referenced a while back in another issue #114 (comment)

Edit:
On a second thought I am not sure if it is a good idea to have a check too. Since the CI now checks the formatting twice, however we could probably replace the nix fmt -- -c command with just checking the pre commit hook.

[pta2002]

Yeah, I'd add the nix fmt -- -c to nix check in that case, and remove it from CI, it's probably for the best

[Alexnortung]

Alright, do you want me to remove it from the CI?

[pta2002]

Yeah, if you need help with that just say though