Set up homes and systems to use cache

home-manager/modules/common.nix

@@ -47,9 +47,11 @@ in
 
       nix = {
         package = mkIf (!(versionAtLeast config.home.stateVersion "22.11")) pkgs.nix;
-        settings = {
+        settings = with lib.my.c.nix; {
           experimental-features = [ "nix-command" "flakes" "ca-derivations" ];
           max-jobs = mkDefault "auto";
+          extra-substituters = cache.substituters;
+          extra-trusted-public-keys = cache.keys;
         };
       };