BroadcastScheduler

We have landed the prototype BroadcastScheduler for improved scaling of DirectView-style message patterns (same request to all engines), but there's still quite a bit to do. Still to do to bring this to maturity:

1. document differences between broadcast and direct view, tuning parameters, etc.
2. ensure broadcast view passes all direct view tests (some noted in skips in test_view_broacast)
3. include benchmarks comparing dview/broadcast
4. consider 'automatic' coalescing behavior rather than explicit
4. when bcast reaches maturity, consider *replacing* directview with broadcast, as it should be better ~across the board, and only worse when everything is super fast (small messages, small number of engines)

Start by reviewing the BroadcastScheduler prototype and the skipped cases in test_view_broacast. Compare the broadcast and direct-view behavior and identify the missing tests, documentation, and benchmarks described in the issue. Done means the listed maturity work has been addressed, including a decision on automatic coalescing and the possible replacement of directview.

Escrita pelo modelo de indexação a partir do texto da issue.