Russia says it has successfully tested an experimental weapon that sounds like something out of a sci-fi movie: a nuclear-powered cruise missile with unlimited range, whose low-flying, terrain-hugging and loitering capabilities could evade American missile defenses and drop atomic bombs anywhere on Earth. Russian President Vladimir Putin said Sunday that the Burevestnik — meaning “storm petrel” (a type of sea bird) — was “indeed a unique weapon that no other country possesses.”