The downgrade code for replicateVectoredInsertsTransactionally currently uses a marker OpTime value of "OpTime::max()" to indicate the oplog chain for a transaction table has been truncated. OpTimes with a timestamp with either component (seconds or inc) with the high bit set result in a full collection scan when searched for, resulting in poor performance with a long oplog.

We can just make this marker optime {{1,0),-1} instead; this will never exist in the oplog because we never write optimes with an inc value of 0.