[PipeSleepStrategy] implement notifySpecific

Implement notifySpecific by using a worker exclusive thread local
sleepState and pipe.
The sleepState previously waitInflight is no longer a member of IoContext
a thread_local PipeSleepStrategy::SleepState is used instead.
It is safe to use a thread_local object because onNewWorkNotification
is only called by the Owner of the sleepState.
Since others (ANYWHERE, EMPER) must not reap newWorkNotifications from
a workers CQ.

Update the algorithm documentation and other code comments.