feat: move nix settings to nix.nix

hosts/matej-nixos/configuration.nix

@@ -24,11 +24,6 @@ in
 
   yubikey.enable = true;
 
-  nix.settings.experimental-features = [
-    "nix-command"
-    "flakes"
-  ];
-
   stylix = {
     enable = true;
     polarity = "dark";

lib/mkHost.nix

@@ -18,22 +18,13 @@ let
     user: import ../users/${user}/home-manager.nix { inherit inputs; }
   );
 
-  gib_in_bytes = 1073741824;
 in
 
 nixpkgs.lib.nixosSystem {
   inherit system;
   modules = [
 
-    {
+    ../nix.nix
-      nix.settings = {
-        download-buffer-size = 1 * gib_in_bytes;
-        experimental-features = [
-          "nix-command"
-          "flakes"
-        ];
-      };
-    }
 
     { nixpkgs.overlays = overlays; }
     { nixpkgs.config.allowUnfree = true; }

nix.nix

@@ -0,0 +1,23 @@
+{
+  nix = {
+    settings = {
+      experimental-features = [
+        "nix-command"
+        "flakes"
+      ];
+      download-buffer-size = 2 * 1024 * 1024 * 1024;
+      warn-dirty = false;
+    };
+
+    gc = {
+      automatic = true;
+      dates = "monthly";
+      options = "--delete-older-than 30d";
+    };
+
+    optimise = {
+      automatic = true;
+      dates = [ "monthly" ];
+    };
+  };
+}