Let’s do the sums. You have a precocious little girl, a child prodigy who speaks to adults with cute sassiness + a custody courtroom battle with emotional speeches + an aggressively insistent soundtrack + the director of The Amazing Spider-Man 2 (Marc Webb). When you run the numbers, Gifted should be insufferable. But it’s not. It’s a minor movie, sure, but a sweet one. Chris Evans plays Frank, a salt of the earth guy who wears baseball caps and fixes boats on the Florida coast and looks after his niece Mary (McKenna Grace), thrust into his care as an infant…