cascade: fix watermark publishing

cascade: fix watermark publishing

* CascadedWorker:
  - fix time comparision in local wm handling
  - publish wm also for leaf nodes
  - fields node_type, node_name, local_watermark were missing in WorkerState
* pgq_node.get_node_info: on leaf node set local watermark to last consumer tick
* pgq_node.set_global_watermark: don't depend on exact code from pgq_node.get_node_info()

Trying to special-case leaf nodes does not seem to be good idea, because
then provider nodes also need to know subscriber node type.  So stop doing it.