If a film such as “The Irishman” or “Once Upon a Time in Hollywood” is unnecessarily long, then what will people say about “Malmkrog,” Cristi Puiu’s three-and-a-half-hour period adaptation? Focused almost entirely on the intellectual discussions of five aristocrats gathered at a wintry Transylvanian mansion in the early 1900s, “Malmkrog” belongs to the milieu of cerebral art-films whose arduousness is perhaps exactly the point.