Kim Cattrall surprised a group of aspiring thespians Monday by popping up in their Columbia University Shakespearean acting workshop. The ex-“Sex and the City” diva practiced reciting lines from the Bard’s “Antony and Cleopatra” for the class. “She said it was for ‘a production in Europe,’ ” said a witness, who added that Cattrall was “amazing” in the role. She’s scheduled to play Cleopatra beginning Sept. 7 at the Chichester Festival Theatre in England.