He was handed the plum of directing two Will Smith vehicles in a row, “The Pursuit of Happyness” (2006) and “Seven Pounds” (2007), and he was able to bring his earthy intelligence and humanity to at least one of them. (The less said about “Seven Pounds” the better.) One way to talk about Muccino’s new film, “Summertime,” which premiered tonight at the 73rd Venice International Film Festival, is to say that he is once again an “Italian filmmaker.” But that wouldn’t be quite accurate. “Summertime” is more like an American film embedded in an Italian one.