Muon's update size remains unchanged under fp16 loss scaling.

The official source reports this update: nightly-last-green: Keep Muon's update at full size under fp16 loss scaling (#8655). Under fp16, Muon parameters barely train with ZeRO-1/2/3 unless the optimizer is offloaded. Newton-Schulz returns the same update at any loss scale, but the step then treats it like a scaled gradient: unscale_and_clip_grads divides it by the loss scale, and the global norm takes it as scaled too. So a Muon parameter moves by 1/loss_scale of its update, 1/65536 with the default dynamic loss scaler.