BRUSSELS — NATO has stayed out of the U.S.-Israeli war in Iran, but the conflict has nevertheless exposed cracks in the alliance’s defenses that would see it struggle if Russia attacks. “The wars in Ukraine and the Middle East are not separate phenomena; there is much to learn from both in thinking about the wars of tomorrow,” Gen. Dominique Tardif, France’s deputy air force chief, said. “These combined lessons should lead us to a better understanding of how to direct capability development.”