Ballista: Avoid sleeping in between polling for tasks

[Dandandan]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
Currently, when polling for work, the executor always waits 250 ms in between polling for tasks.
This means if the tasks themselves are small, it can be unproductive for a large percent of the time.

We can track whether we received tasks in the last iterations to avoid sleeping.

Also a slightly lower sleep time (e.g. 100ms) can help reduce the initial delay.

Describe the solution you'd like
Track whether we received tasks in the last iterations to avoid sleeping.

Describe alternatives you've considered
n/a

Additional context
n/a