If you're a horror fan with an Apple TV+ subscription, you simply must be watching Servant, an ickily slow-burning psychological horror series from executive producer/director M. Night Shyamalan and writer/creator Tony Basgallop (What Remains). In artfully composed half-hour episodes, Servant tells the tale of parents Dorothy and Sean Turner (Lauren Ambrose and Toby Kebbell) who've recently, tragically lost a child. To cope, Dorothy takes care of an eerily lifelike doll, pretending it's her real baby. And when this coping mechanism extends as far as hiring a real-life nanny (Nell Tiger Free), things …