readSnapshotTailApart
suspend fun EventLog.readSnapshotTailApart(ref: AggregateRef, snapshots: SnapshotStore, earlier: Int): SnapshotTail
ref's snapshot in snapshots and the tail after it, read apart: SnapshotStore.load, then EventLog.readTail from the snapshot's version, or every stream of ref (a replay) and no earlier keys when there is no snapshot.