NEW YORK — A few hours before his fall runway show, Oscar de la Renta sat elegantly in a high-backed chair oblivious to the leggy models in hair curlers and the frantic stylists. It was as if the world were in rapid motion, while the impeccably dressed designer sat quietly enjoying his solitude.  “Being
 calm is just on the surface,” he said with a chuckle. “When you know 
that you've done your very best, that's all you can do.”