It was a meaningless hit-and-giggle session, a mixed doubles exhibition at Rod Laver Arena just for fun and charity in front of fans a few days ahead of the Australian Open, so Coco Gauff was calling out how fast she would try to hit some serves. Yes, she has — on her serving and her forehand — and the strides made in both of those areas are among the reasons Gauff is considered one of the few women ready to challenge two-time defending champion Aryna Sabalenka for the title at Melbourne Park when the year’s first Grand Slam tournament begins Sunday (Saturday EST).