nix: set CMake version to 3.30.4

game/src/game.cxx

@@ -0,0 +1,22 @@
+// Global module fragment, where #includes can happen
+module;
+
+import std;
+
+export module game;
+
+export class lib
+{
+public:
+    lib();
+    ~lib();
+    void helloworld();
+};
+
+lib::lib() = default;
+lib::~lib() = default;
+
+void lib::helloworld()
+{
+    std::print("Hello world!\n");
+}