Switch to flake-based build on nix-builder for nightly rust.

nix/configuration/flake.nix

@@ -29,6 +29,10 @@
       url = "github:nix-community/disko";
       inputs.nixpkgs.follows = "nixpkgs";
     };
+    nix_builder = {
+      url = "git+https://code.fizz.buzz/talexander/nix_builder.git";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
   };
 
   outputs =
@@ -39,6 +43,7 @@
       disko,
       impermanence,
       lanzaboote,
+      nix_builder,
       ...
     }:
     let
@@ -70,7 +75,7 @@
         hostname: nodeConfig: format:
         nixpkgs.lib.nixosSystem {
           specialArgs = {
-            inherit self;
+            inherit self nix_builder;
 
             this_nixos_config = self.nixosConfigurations."${hostname}";