NEW YORK (AP) — David Fincher’s “Mank” is such a dense and dazzling Hollywood time machine that all the conversation it’s spawned has sometimes overlooked the incredible balancing act at its center. Gary Oldman’s performance is always teetering on the edge, poised between inebriation and lucidity, ’40s-style zip and modern-day naturalism. In an interview, Oldman says he had to draw on his own “muscle memory” as an alcoholic. In crafting the portrait of “Citizen Kane” co-writer Herman Mankiewicz, Fincher wanted Oldman as himself. No wigs, no special costume. For Oldman, who won an Oscar for his Winston Churchill in “Darkest Hour,” that made him nervous.