Once upon a time there was a very cold war.Rivulets of intrigue, repression and intolerance twined the cultural landscape. On the outskirts of the nation’s capital, defense research laboratories whirred away in secrecy. And it is here, in the unlikely setting of post-Sputnik Baltimore, that Guillermo del Toro’s sensuous sci-fi fable “The Shape of Water” takes place.Inspired by “Creature From the Black Lagoon,” both movies’ love-struck amphibians hail from the Amazon and bear a …