fix(historian): #686 review — bounded, density-aware reverse raw walk; uncapped Gateway raw reads

1. Uncapped reverse raw read on a forward-only backend = ONE forward read of the
   window, filtered and reversed in memory (was a segment-by-segment walk).
2. Segment width is aimed at ~half the row budget from the density just observed
   (overflow: from the truncated read's own sample span) and carried page to page
   in HistoryContinuationState.SegmentWidthTicks.
3. The walk starts no later than now + 1 day and never reads before the epoch.
4. Request bounds are rounded outward to the millisecond, so a row AVEVA
   fabricates at a rounded-up query start cannot land inside the segment.
5. Budget M = max(1, MaxTieClusterOverfetch); reads ask M + 2 rows, completeness is
   'short OR last row past the segment', and a read crowded by rows before the
   segment is re-read once (<= 2M + 4). A cluster of exactly M, neighbouring
   clusters each within M, and M <= 1 are all served; only one timestamp over M
   is refused. ServerHistorianOptions text updated.
6. The raw and events tie-path oversized-cluster refusal is BadTooManyOperations
   (was BadHistoryOperationUnsupported), consistent with the walk.
7. GatewayHistorianDataSource.ReadRawAsync: a caller cancellation is not a backend
   failure; NumValuesPerNode = 0 is sent as int.MaxValue (the client package and
   the gateway reject max_values <= 0, so every uncapped Gateway raw read failed);
   a MaxValuesCeiling refusal is a HistoryReadLimitExceededException.
8. Tests: upper-edge filter, epoch floor, look-ahead, ms alignment, exact/adjacent
   clusters, minimal budget, carried density, and the walk over the real Gateway
   source + FakeHistorianGatewayClient (OpcUaServer internals visible to it).

tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/NodeManagerHistoryReadEventsPagingTests.cs

@@ -69,7 +69,7 @@ public sealed class NodeManagerHistoryReadEventsPagingTests : IDisposable
         var p1 = ReadEvents(nm, node, max: 3, inboundCp: null);
         p1.Cp.ShouldNotBeNull();
         var p2 = ReadEvents(nm, node, max: 3, inboundCp: p1.Cp);
-        p2.Error.StatusCode.Code.ShouldBe(StatusCodes.BadHistoryOperationUnsupported);
+        p2.Error.StatusCode.Code.ShouldBe(StatusCodes.BadTooManyOperations);
         await host.DisposeAsync();
     }
 
@@ -283,7 +283,7 @@ public sealed class NodeManagerHistoryReadEventsPagingTests : IDisposable
         var p1 = ReadEvents(nm, node, max: 3, inboundCp: null, end: Early, start: Late);
         p1.Cp.ShouldNotBeNull();
         ReadEvents(nm, node, max: 3, inboundCp: p1.Cp, end: Early, start: Late).Error.StatusCode.Code
-            .ShouldBe(StatusCodes.BadHistoryOperationUnsupported);
+            .ShouldBe(StatusCodes.BadTooManyOperations);
         await host.DisposeAsync();
     }