Dask on Ray API

For usage, see Using Dask on Ray.

RayDaskCallback	Extends Dask's Callback class with Ray-specific hooks.
_ray_presubmit	Run before submitting a Ray task.
_ray_postsubmit	Run after submitting a Ray task.
_ray_pretask	Run before executing a Dask task within a Ray task.
_ray_posttask	Run after executing a Dask task within a Ray task.
_ray_postsubmit_all	Run after Ray submits all tasks.
_ray_finish	Run after Ray finishes executing all Ray tasks and returns the final result.