pulse: busy loop when evenly introducing work

When evenly introducing work the sleep continuation of the pulser fiber
is possibly delayed due to the worker executing an introduced work items
distorting the pulse.

This distortion does not occure when the pulser busy loops between
introducing work items. We do not count the busy looping worker running
the pulser when calculating the work items to reach the target utilization.
51 jobs for improve-even-pulse in 25 minutes and 19 seconds (queued for 3 seconds)