NIFI-16130 - Fix ReplayLastEventEndpointMerger to count per-node replays correctly

[pvillard31]

Summary

NIFI-16130 - Fix ReplayLastEventEndpointMerger to count per-node replays correctly

Provenance event IDs are local counters per node, starting at 0 and incrementing independently. In a multi-node cluster two different nodes can legitimately have the same numeric event ID for entirely different physical provenance events.

ReplayLastEventEndpointMerger was using a HashSet<Long> to accumulate event IDs returned by each node after a "replay last event" request. Because both nodes in a 2-node cluster where each has processed the same number of events will return the same local event ID, the HashSet silently deduplicated them and reported eventsReplayed.size() == 1 instead of 2. This caused ClusteredReplayProvenanceIT.testReplayLastEvent (with ReplayEventNodes.ALL) to fail with expected: <2> but was: <1>.

Change: Replace HashSet<Long> with ArrayList<Long> for the event ID accumulator so each node's replay is counted independently regardless of matching local event IDs.

Also adds: ReplayLastEventEndpointMergerTest — there was no unit test for this merger class. The test covers the colliding-ID case (regression test for this fix), the distinct-ID case, and the partial-failure case.

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[exceptionfactory]

Thanks @pvillard31, the functional change to List<Long> for Provenance IDs looks good. For the new test, the public modifiers can be removed, and it looks like static values, as well as the NodeIdentifier objects themselves, could be declared once as static final members.

[exceptionfactory]

Thanks @pvillard31, the latest version looks good.