feat(nix): add rebuild script for when local cache is down

common/modules/cachix.nix

@@ -1,4 +1,18 @@
-{...}: {
+{
+  config,
+  pkgs,
+  ...
+}: {
+  environment.systemPackages = with pkgs; [
+    (writeShellApplication {
+      name = "rebuild-no-cache";
+      runtimeInputs = [config.nh.package];
+      text = ''
+         nh os switch -- --option binary-caches "https://cache.nixos.org" "$@"
+      '';
+    })
+  ];
+
   nix = {
     settings = {
       substituters = [