feat: implement CPP02 C++20 card

src/task03/main.cpp

@@ -0,0 +1,7 @@
+#include <iostream>
+enum class State { idle, ready };
+struct Sample { int value; State state; };
+int main() {
+    Sample sample{23, State::ready};
+    std::cout << "sample=" << sample.value << " state=" << (sample.state == State::ready ? "ready" : "idle") << '\n';
+}