feat: implement CPP02 C++20 card

src/task02/main.cpp

@@ -0,0 +1,8 @@
+#include <iostream>
+constexpr int square(int value) { return value * value; }
+int main() {
+    constexpr int result = square(7);
+    const int limit{12};
+    static_assert(result == 49);
+    std::cout << "square=" << result << " limit=" << limit << '\n';
+}