one can now give tasks an optional string "name". If `Trace`
is present (installed) and enabled, this results in
a span around the task's execution. This also plays ok
with `await` and other effect-based primitives.
there's a single blocking queue, and one WS_queue per worker. Scheduling
into the pool from a worker (e.g. via fork_join or explicitly) will push
into this WS queue; otherwise it goes into the main blocking queue.
Workers will always try to empty their local queue first, then try to
work steal, then block on the main queue.
