We’re very much looking forward to seeing the new HBO biopic “Phil Spector,’’ writer/director David Mamet’s movie about the legendary — and legendarily eccentric — music producer. The film about the pioneering producer — Spector created the technique known as “the wall of sound’’ — costars Al Pacino and British actress Helen Mirren, who plays Linda Kenney Baden, the attorney who defended Spector in his murder trial. (That didn’t work out too well because Spector is currently serving 19 years to life for killing actress Lana Clarkson.) But keep an eye out also for Ella Dershowitz, daughter of Harvard Law professor Alan Dershowitz. She plays Mirren’s legal assistant in the movie debuting March 24.