Leigh Bardugo has made a career out of writing about oppressed people who wield uncanny powers. Those concerns loom large in her young-adult Grishaverse series, about a downtrodden minority who command a world-shaping magic, and the hero of her adult debut, “Ninth House,” is also lifted up from poverty thanks to unique abilities. But her latest adult novel, “The Familiar,” explores this theme with an even greater depth and sensitivity.