Mercedes are putting academy driver Kimi Antonelli through his paces in an extensive private testing programme. The Silver Arrows want to establish whether he’s ready for a full-time race seat in 2025. Toto Wolff, of course, needs to find a replacement for seven-time world champion Lewis Hamilton. He’s known since the winter that Hamilton was headed to Ferrari for 2025. Wolff says Antonelli is a contender for the seat but Nico Rosberg has cautioned that it may be too early for a driver who won’t turn 18 until August. The Italian is trying to quash those doubts. Mercedes will be keeping a close…