By THÉRÈSE MARGOLIS Mexico’s City’s premiere Sicilian restaurant, María 138, turned six on Thursday, Aug. 25, and its owner, Cristina Maria Cialona, in true Sicilian (and true Cristina Maria Cialona) style, celebrated the occasion with an “intimate” gathering of some 150 of her closest friends, with a lavish night of pizza and prosecco Bellinis. And also true to Cristina Maria