feat(nixos): add terraria and gamemode services and update configurations

nixos/ryu/programs/default.nix

@@ -8,5 +8,6 @@
     ./obs-studio.nix
     ./gnome-disks.nix
     ./nix-ld.nix
+    ./gamemode.nix
   ];
 }

nixos/ryu/programs/gamemode.nix

@@ -0,0 +1,5 @@
+{...}: {
+  programs.gamemode = {
+    enable = true;
+  };
+}

nixos/ryu/programs/steam.nix

@@ -4,10 +4,17 @@
     gamescopeSession.enable = true;
     remotePlay.openFirewall = true;
     dedicatedServer.openFirewall = true;
+    localNetworkGameTransfers.openFirewall = true; # Open ports in the firewall for Steam Local Network Game Transfers
     extraCompatPackages = [
       pkgs.proton-ge-bin
+      pkgs.gamescope
+      pkgs.mangohud
     ];
   };
+  programs.gamescope = {
+    enable = true;
+    capSysNice = true;
+  };
   environment.systemPackages = [
     pkgs.protonup-qt
   ];