Now playing at the Nichols Library:   Son of Saul, a concentration camp drama that won the Oscar for best foreign language film;  Heart of the Sea, a story of shipwreck and survival, Lady in the Van, a comedy of manners featuring Maggie Smith (Downton Abbey), Jane got a Gun, a western in which a woman defends her home against outlaws,  and Prime Cut, a cult suspense classic featuring Lee Marvin, Gene Hackman and a young Sissy Spacek.