Changes to rpi setup

modules/common.nix

@@ -11,10 +11,20 @@
   nix = {
     settings = {
       experimental-features = [ "nix-command" "flakes" ];
-      # Save disk space on Pi
       auto-optimise-store = true;
+      # Extra binary caches — speeds up aarch64-linux builds significantly
+      substituters = [
+        "https://cache.nixos.org"
+        "https://nix-community.cachix.org"
+        # Pre-built RPi vendor kernel + firmware (linuxPackages_rpi4, etc.)
+        "https://nixos-raspberrypi.cachix.org"
+      ];
+      trusted-public-keys = [
+        "cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY="
+        "nix-community.cachix.org-1:mB9FkXj6Q3Q4ohOcbM4FJ9Z1X2kCrVK4vZOqsDqqNqk="
+        "nixos-raspberrypi.cachix.org-1:4iMO9LXa8BqhU+Rpg6LQKiGa2lsNh/j2oiYLNOQ5sPI="
+      ];
     };
-    # Weekly garbage collection — keeps the system from filling the SD card
     gc = {
       automatic = true;
       dates     = "weekly";
@@ -113,5 +123,5 @@
   # System state version — do not change after first install
   # (tracks NixOS backwards-compat markers)
   # -------------------------------------------------------------------------
-  system.stateVersion = "24.11";
+  system.stateVersion = "25.05";
 }