feat(nixosmodules): add steam module

modules/nixos/gaming.nix

@@ -0,0 +1,42 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+let
+  moduleName = "gaming";
+  cfg = config."${moduleName}";
+in
+{
+  options = {
+    "${moduleName}" = {
+      steam = {
+        enable = lib.mkEnableOption "Enable Steam.";
+        enableGamescope = lib.mkEnableOption "Enable the gamescope compositor.";
+      };
+    };
+  };
+
+  config = lib.mkMerge [
+    (lib.mkIf cfg.steam.enable {
+      programs.steam = {
+        enable = true;
+        remotePlay.openFirewall = true; # Open ports in the firewall for Steam Remote Play
+        protontricks.enable = true;
+        dedicatedServer.openFirewall = true; # Open ports in the firewall for Source Dedicated Server
+        localNetworkGameTransfers.openFirewall = true; # Open ports in the firewall for Steam Local Network Game Transfers
+      };
+      environment.systemPackages = with pkgs; [
+        steam-run
+      ];
+    })
+    (lib.mkIf cfg.steam.enableGamescope {
+      programs.steam.gamescopeSession.enable = true;
+      programs.gamescope = {
+        enable = true;
+        capSysNice = true;
+      };
+    })
+  ];
+}