Naomi Osaka’s appearance at this May’s Met Gala in New York – which she wittily dubbed “the grand slam of fashion” – was a whirlwind business engagement jammed between two of tennis’s major tournaments. With stacked schedules, tennis superstars are usually found taking ice baths between events. Not Osaka, who donned a 9kg Robert Wun couture gown in response to the Met’s “fashion is art” theme. Her presence at the Met Ball was more than a celebri…