“Pachinko,” a beautifully wrought historical melodrama, is back for its necessary second season, to fill in some holes, fiddle with loose ends and extend the story even farther beyond the borders of Min Jin Lee’s 2017 novel. It is a transitional season, which ends with little resolved and gaps still to fill, and while it offers all the sensual pleasures of the first season’s performances and production, its portion of love and death, it is very much the middle of a book. Unlike the novel, which proceeds chronologically, the series, returning Friday on Apple TV+, alternates between the “present…