Migrate to snowfall lib

modules/nixos/system/nix/default.nix

@@ -0,0 +1,27 @@
+{ pkgs, ... }: {
+  nix = {
+    package = pkgs.nixFlakes;
+    extraOptions = ''
+      experimental-features = nix-command flakes
+      warn-dirty = false
+      keep-outputs = true
+      keep-derivations = true
+    '';
+    gc = {
+      automatic = true;
+      dates = "weekly";
+      options = "--delete-older-than 7d";
+    };
+    settings = {
+      auto-optimise-store = true;
+      builders-use-substitutes = true;
+      substituters =
+        [ "https://hyprland.cachix.org" "https://cache.nixos.org" ];
+      trusted-public-keys = [
+        "hyprland.cachix.org-1:a7pgxzMz7+chwVL3/pzj6jIBMioiJM7ypFP8PwtkuGc="
+        "cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY="
+      ];
+    };
+  };
+  system.stateVersion = "23.05";
+}