Moonpool_private.Ws_deque_SourceWork-stealing deque.
Adapted from "Dynamic circular work stealing deque", Chase & Lev.
However note that this one is not dynamic in the sense that there is no resizing. Instead we return false when push fails, which keeps the implementation fairly lightweight.
Deque containing values of type 'a
Push value at the bottom of deque. returns true if it succeeds. This must be called only by the owner thread.
Pop value from the bottom of deque. This must be called only by the owner thread.