Use pkgs from inputs, not `callPackage`

[ldicarlo]

I think that since you are using
default = pkgs.callPackage ./package.nix {};
It uses the one from the host.
Since you are using nixpkgs-unstable and a more recent version of rust than the one in nixpkgs-stable, it leads to conflicts.

I am not sure of the solution though, I usually don't use an intermediary file for packages.

To build it, on my side I need to do:

services.ncro = {
  enable = true;
  package = inputs.ncro.packages.${pkgs.system}.default;
  settings = { ... };
};