Unfolding beneath skies the color and density of damp concrete, “Loveless,” the fifth feature from the Russian director Andrey Zvyagintsev (after his notable 2014 drama, “Leviathan”), uses a toxic marriage to paint a larger portrait of decay, dereliction and moral detachment. And oh, his gaze is pitiless. Set in Moscow in the autumn of 2012, the picture sits on the screen with an almost physical weight, its heaviness as much to do with the bleakly beautiful visuals and painstaking pacing as the bitter divorce at its center. Boris and Zhenya (Alexey Rozin and Maryana Spivak) loathe each other, their vitriol...