fix(historian): #691.4 review — uncapped Gateway events reads no longer pre-size to int.MaxValue

GatewayHistorianDataSource.ReadEventsAsync sized its result list to
maxEvents, which is int.MaxValue for NumValuesPerNode = 0: every
uncapped Gateway events read (forward on master, and the new walked
reverse one) threw 'Array dimensions exceeded' and counted as a backend
failure. Capacity is bounded at 1024. The events walk delegate moved to
ReverseEventsReader so it is tested over the real Gateway source
(forward uncapped, reverse uncapped, reverse capped).

src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/OtOpcUaNodeManager.cs

@@ -5311,22 +5311,9 @@ public sealed class OtOpcUaNodeManager : CustomNodeManager2
                 // Walk for one more than the fetch: finding it is the "more events exist" signal a source gives with its
                 // continuation point (the walk itself cannot flag truncation).
                 var want = numValuesPerNode == 0 ? 0u : (uint)Math.Min(uint.MaxValue - 1L, (long)fetch + 1);
-                var budget = Math.Max(1, MaxTieClusterOverfetch);
-                var walkSource = sourceName;
-                var (rows, next) = await ReverseWalk.WalkAsync<HistoricalEvent>(
-                        async (s, e, cap, token) =>
-                        {
-                            var r = await source.ReadEventsAsync(walkSource, s, e, cap == 0 ? int.MaxValue : cap, reverse: false, token)
-                                .ConfigureAwait(false);
-                            return new ForwardSegmentRead<HistoricalEvent>(r.Events, r.ContinuationPoint is not null);
-                        },
-                        ev => ev.EventTimeUtc.Ticks, EventIdTieOrder.Instance, startUtc, endUtc, want, budget,
-                        source.TimestampResolutionTicks, Clock.GetUtcNow().UtcDateTime, walkHint,
-                        at => new HistoryReadLimitExceededException(budget,
-                            $"A reverse events read of '{walkSource}' at {at:O} found more than {budget} events at one " +
-                            "timestamp; the backend reads forward only, so the latest of them cannot be selected. Increase " +
-                            "ServerHistorian:MaxTieClusterOverfetch."),
-                        ct)
+                var (rows, next) = await ReverseEventsReader.ReadAsync(
+                        source, sourceName, startUtc, endUtc, want, MaxTieClusterOverfetch, Clock.GetUtcNow().UtcDateTime,
+                        walkHint, ct)
                     .ConfigureAwait(false);
                 walkHint = next;
                 var more = want > 0 && rows.Count > fetch;