[Move] Implement << operator

Move.cpp

@@ -39,7 +39,10 @@ std::optional<PieceType> Move::promotion() const {
 }
 
 std::ostream &operator<<(std::ostream &os, const Move &move) {
-    (void) move;
+    os << move.from() << move.to();
+    if (move.promotion().has_value()) {
+        os << static_cast<char>(move.promotion().value());
+    }
     return os;
 }