[tracing] Enqueue processing 1 by 1 after the response has been sent.
[tracing] Enqueue processing 1 by 1 after the response has been sent.

Scheduling each span to be processed only after a previous one has been
finished means that other code gets a chance to also schedule work in
between.

mzikherman/metaphysics-1,mzikherman/metaphysics-1,artsy/metaphysics,craigspaeth/metaphysics,artsy/metaphysics,craigspaeth/metaphysics,mzikherman/metaphysics-1,artsy/metaphysics,mzikherman/metaphysics-1