chore: add formatter

[limwa]

Hi, I noticed that the project uses nixpkgs-fmt in its devShells, but doesn't set a formatter in the flake. I thought it could be useful to set it, and while I'm at it, I also decided to add an action that checks the formatting of all files.

1. Adds nixpkgs-fmt as the formatter in the flake. Makes it so that nix fmt . automatically invokes nixpkgs-fmt.
2. Adds a GH action that checks the formatting of all files in the project on every PR and push to develop or main.
3. Formats all unformatted files to comply with the requirements imposed by the action.

[limwa]

I just noticed that nixpkgs-fmt has been archived (https://github.com/nix-community/nixpkgs-fmt), so I replaced it with nixfmt. nixfmt-tree is the recommended way of invoking nixfmt for an entire project, it seems.

[doronbehar]

@nvmd could we please make a bit of progress regarding the formatting? This PR, and:

• modules: add enable option guards #152
• Cross-compilation support, broken into small incremental commits #163
• ci: test doc generation for modules #177

All try to format the project and it is a mess. I'm trying to merge multiple pull requests locally to test them and help with the project in general but it becomes too hard with all the merge conflicts related to formatting.

[limwa]

I was looking at the other PRs you mentioned and saw that you suggested adding a .git-blame-ignore-revs file like in nixpkgs. I can do that here too later today!

[limwa]

I've added the .git-blame-ignore-revs file and I've also rebased the PR to resolve the merge conflicts.

[nvmd]

Hi @doronbehar thanks for bringing this issue up. The formatting does seem like a hot topic indeed.

However, regardless of how hot it is, I can't for the sake of further maintainability merge it together with some irrelevant changes. The examples you include here: mix formatting with the other changes on the commit level, effectively hiding them; formatting being a part of a PR otherwise needed review feature by feature. This feedback was provided to the authors of the corresponding PRs.

That said, I don't quite understand the pressure you're trying to put on me personally. Though I guess it's done with good intentions and your help with the project would be greatly appreciated in any case.

[nvmd]

I've added the .git-blame-ignore-revs file and I've also rebased the PR to resolve the merge conflicts.

Thanks @limwa! I did completely forget about this feature! And this PR being the cleanest of the formatting ones, sorry! No any more questions from my side.

[doronbehar]

Thanks @nvmd :). Hope to be able to further help soon with testings.