Princeton, NJ, has become the Hollywood of the Garden State this week since “Runner Runner,” Ben Affleck’s new movie also starring Justin Timberlake, Anthony Mackie and Gemma Arterton, came to town. Spies saw some of the stars filming at the Ivy Inn, a famous watering hole usually populated by students, and at PJ’s Pancake House, a popular haunt for preppies and parents to visit. The film by “Ocean’s Thirteen” and “Rounders” writers Brian Koppelman and David Levien was shot in (perhaps more exotic) Puerto Rico over the summer. The cast has also been spotted in the town’s Palmer Square, sipping java.