Applying a minute and painterly eye to ordinary lives encircled by much larger circumstance — be it a motorway as in 2013’s Golden Lion-winning “Sacro Gra,” or the seaborne migrant crisis as in 2016’s Golden Bear-winning “Fire at Sea” — has led to Italian-American director Gianfranco Rosi’s most celebrated documentaries. But in “Notturno,” his return to the Venice competition, the approach is stretched a little beyond its elastic limit, proving only a fitful, if often spectacular, match for a thematic backdrop as grand, complex and intractable as [sweeping gesture] Middle East conflict.