Kit Harington already played Gilderoy Lockhart. He recorded the entire role for Audible's full-cast Harry Potter audiobooks last December, months before HBO ever called. That detail explains how the fastest recast in franchise TV just happened. Nicholas Hoult was announced as Lockhart earlier this month. Two weeks later the production schedule shifted, his Superman sequel dates collided, and HBO let him out of his deal. Most shows would spend months re-auditioning. HBO had a finished…