Checks that the sequenced events' sequencer counters are a gap-free increasing sequencing starting at firstSequencerCounter and their timestamps increase strictly monotonically. When a violation is detected, an error is logged and the processing is aborted.

This is normally ensured by the com.digitalasset.canton.sequencing.client.SequencedEventValidator for individual sequencer subscriptions. However, due to aggregating multiple subscriptions from several sequencers up to a threshold, the stream of events emitted by the aggregation may violate monotonicity. This additional monotonicity check ensures that we catch such violations before we pass the events downstream.