Pitchers Ryan Helsley and Tyler Rogers and outfielder Cedric Mullins jumped into a pennant race Friday when they joined the National League-East leading New York Mets in search of the franchise’s first championship since 1986. “Everybody’s very excited — they’re matching my excitement to be here,” Rogers said before the Mets opened a three-game series against San Francisco. The Giants traded Rogers to New York for José Buttó and a pair of prospects Wednesday.