Using @attrs for the flake was cool at first, but this doesn't actually
work if we want to use our nix-config inside NixOS containers due to how
`self` works.
Because of this, it's easier to simply ban @attrs altogether and use
`nix-config` for everything since it's possible to access *all* the
inputs of nix-config from itself instead of having to manually inherit
each input we want (which could be any of them).
This fixes an issue where previously homeManagerModules would be an
unknown flake output. Note that this change is a part of Nix 2.22.3
but not Nix 2.23.3.
This fixes an issue where previously the derivation had to be evaluated
before importing the base16 scheme, thus causing `nix flake check` to
fail when multi-platform support was added.
See: https://github.com/NixOS/nix/issues/4265
