Simplify TransportBroadcastByNodeAction (#93484)

Similarly to #92987, recent improvements to the primitives for writing
async code (particularly #92452 and #92620) mean that we can enormously
simplify `TransportBroadcastByNodeAction`. In particular, we can avoid
accumulating an intermediate array of responses for later processing in
favour of just accumulating the successes and failures into their final
separate lists. We also no longer need to use a separate
`NodesResponseTracker` to discard responses on cancellation. Finally, we
can now discard shard-level responses more promptly on cancellation.

Author: DaveCTurner