chore(cheetah)!: update config

Use flake overlays in `mkNixOnDroidHost`
Fix `FireCode` `ttf` path in `terminal.font`
Use `pkgs.nixUnstable`

machines/nix-on-droid/aarch64-linux/cheetah/configuration.nix

@@ -23,6 +23,8 @@
     keep-derivations = true
   '';
 
+  nix.package = pkgs.nixUnstable;
+
   time.timeZone = "Europe/Sofia";
 
   terminal.font =
@@ -30,7 +32,7 @@
       firacode = pkgs.nerdfonts.override {
         fonts = [ "FiraCode" ];
       };
-      fontPath = "share/fonts/truetype/NerdFonts/Fira Code Regular Nerd Font Complete Mono.ttf";
+      fontPath = "share/fonts/truetype/NerdFonts/FiraCodeNerdFontMono-Regular.ttf";
     in
     "${firacode}/${fontPath}";
 }

util/default.nix

@@ -136,7 +136,7 @@ rec {
     pkgs = import nixpkgs {
       inherit system;
 
-      overlays = [
+      overlays = builtins.attrValues outputs.overlays ++ [
         inputs.nix-on-droid.overlays.default
       ];
     };