D aniel Radcliffe is dallying on his lunch break from a Broadway rehearsal, but he’s not concerned about being late. “I’m literally the only person in this play,” says the actor, 36, on a phone call from Manhattan’s Theater District. “They can’t start without me.”  It’s the third day of rehearsals for Every Brilliant Thing , beginning Feb. 21, a one-man show that sees Radcliffe’s character create a list of reasons life is worth living in an effort to help his suicidal mother. The performance