An icy-hot paradox of a film, and one of the year’s peak achievements, writer-director Todd Field’s “Tár” casts a gimlet eye on a fictional American orchestra conductor and composer, Lydia Tár, at the summit of her global fame. The view is glorious. It’s also more treacherous than she realizes. Cate Blanchett, for whom Lydia was written and the reason, Field acknowledges, the movie got made, goes to town and back again in this role. In the past, Blanchett often has added an extra 10% to a performance that takes it to 110%, as in her Oscar-winning turn in Woody Allen’s “Blue Jasmine,” simply be…