@Override
  public <K> void scheduleCallback(K key, long timestamp, ScheduledCallback<K> callback) {
    this.epochTimeScheduler.setTimer(key, timestamp, callback);
  }
Delegates to {@link EpochTimeScheduler}. This is useful because it provides a write-only interface for user-facing
purposes.
samza-core/src/main/java/org/apache/samza/scheduler/CallbackSchedulerImpl.java