add nix settings for darwin

platforms/nixos/modules/nmasur/presets/services/nix.nix

@@ -45,6 +45,7 @@ in
         trusted-users = [
           "root"
           "@wheel"
+          username
         ];
 
         # Add community Cachix to binary cache
@@ -57,9 +58,7 @@ in
           "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
         ];
 
-        # Scans and hard links identical files in the store
-        # Not working with macOS: https://github.com/NixOS/nix/issues/7273
-        auto-optimise-store = lib.mkIf (!pkgs.stdenv.isDarwin) true;
+        auto-optimise-store = true;
       };
 
     };