Barry Zito is a class act. In an era of oversized sports egos, what other major league star would take out a full-page ad in the newspaper to thank his fans, his teammates, and those lowly sports writers? The ad appears in today’s San Francisco Chronicle sports section. And Zito isn’t even really leaving. The A’s former star pitcher is just moving across the bay to the San Francisco Giants after signing one of the most lucrative contracts in baseball history.