[BUG] Support multiple delayed outbounds for a single txn

A bug was discovered in testnet where a single outbound was split into multiple, but then delayed at different block heights. This causes the observation of the each outbound to not correlate to a txout item, hence causing a false negative and slashed node operators.

With this change, when an outbound is split into multiple, it all gets sent out in the same block height, choosing the highest calculated height.

In addition, the observed tx vote struct has a new attribute called OutboundHeight, which records the height in when an outbound was originally scheduled.