The initialization of a `SyncAggregate` to its default value is not very
intuitive. There is an `init` function in `sync_committee_msg_pool` that
provides a convenience wrapper. This patch exports that initializer so
that the rest of the code base can also take advantage of it.
There are still a few cases with manual loops through sync subcommittees
even though an `allSyncCommittees` iterator exists. Adjusted the few
remaining instances to also use the iterator instead.
* Placing callbacks into strategic places.
* Initial events call implementation.
* Post rebase fixes.
* Change addSyncContribution() implementation.
* Add `attestation-sent` event.
Remove gcsafe, raises from callbacks implementations.
Move `attestation-received` fire at the end of attestation processing.
* Address review comments.
Etan Kissling
Eugene Kabanov
Zahary Karadjov
tersec