dfmt: init

[ipsavitsky]

This change adds popular dlang formatter dfmt

[ipsavitsky]

this depends on dfmt getting built in nixpkgs-unstable from main. This MR will also require update of the flake input

This is tracked https://nixpk.gs/pr-tracker.html?pr=401429

[ipsavitsky]

dfmt is released, so this change is ready for review

[zimbatm]

blocked on CI

[ipsavitsky]

@zimbatm I've managed to satisfy ci, but I had to mark 2 packages as broken for darwin. Should this be merged or should we wait until a more stable nixpkgs ref where zig and/or actionlint are fixed?

[zimbatm]

thanks! maybe just notify the maintainers of the packages, that should be enough