Minor bug fix: changing train_step in examples code to take a mean of the stats instead of taking from the first device. Because the optimizer syncs its own stats (like loss), this didn't matter except for stats returned from the kfac_jax optimizer (or Optax optimizers using OptaxWrapper). However, the Polyak averaged loss wasn't actually synced across devices (as its not part of the optimizer anymore), so "loss_polyak" was being reported only for the first device.

Minor bug fix: changing train_step in examples code to take a mean of the stats instead of taking from the first device. Because the optimizer syncs its own stats (like loss), this didn't matter except for stats returned from the kfac_jax optimizer (or Optax optimizers using OptaxWrapper). However, the Polyak averaged loss wasn't actually synced across devices (as its not part of the optimizer anymore), so "loss_polyak" was being reported only for the first device. #1524