This was an “anything goes” week for the world’s most stylish, but one in which everything (even the most outrageous slits and volumes) looked utterly effortless. From tribal to trouser suit to trench, these ladies slayed. Solange Knowles (in Shanel and Y/Project) took an avant-grade approach to body-con for Parsons’s annual gala. FKA twigs made vintage Jean Paul Gaultier daywear seem just right for a big night out. Metallics had a moment: on Paloma Elsesser in Molly Goddard’s voluminous…