Reduce On Plateau Learning Rate Scheduler
Source:R/CallbackSetLRScheduler.R
      mlr_callback_set.lr_scheduler_reduce_on_plateau.RdReduces the learning rate when the first validation metric stops improving for patience epochs.
Wraps torch::lr_reduce_on_plateau()
Super classes
mlr3torch::CallbackSet -> mlr3torch::CallbackSetLRScheduler -> CallbackSetLRSchedulerReduceOnPlateau