The classical music world is so tightly guarded, so underreported on, and so frustratingly predictable that surprises are rare. Yet, in the past month, Anthony Tommassini has found himself stunned by no fewer than three announcements from some of the world’s top classical figures. The New York Philharmonic’s surprise move to Carnegie Hall is, of course, at the top. Second on the list: the Cleveland Orchestra’s decision to extend the contract of its young and (some say) unproven music director through 2012 after only one year on the job. And last, but not even remotely least, there is the stunning news that Luciano Pavarotti has scheduled a farewell performance at the Met. Again. And he promises to show up this time.