MIDWAY THROUGH THE FIRST ACT of Decision to Leave, Park Chan-wook’s new film, a split-second gesture baits the senses: Alone with a woman late at night, a man unfastens his belt, its frictional hiss lancing the room’s tense silence. But the loaded cue dissolves in the same instant, as he reaches for a leather holster and fastens it to the belt. In the next scene, he’s cooking her dinner. No other filmmaker could so swiftly cram three seconds with as many successive feelings: a nascent thrill, its swerve into frustration, and its sudden detour into confusion, seeming too brief to have happened