fix(historian): #693 AtTime type hint — Boolean nodes stepped, integer nodes rounded to their type

Review follow-up: on the Gateway every value is a Double (AVEVA stores a Boolean
as a 0/1 Int2), so the raw-evaluated AtTime interpolated a Boolean node to 0.5.

- IHistorianDataSource gains a default-interface overload
  ReadAtTimeAsync(fullReference, timestamps, TypeCode? valueType, ct) that
  forwards to the existing one (SqlServer/QuestDB/Null/fakes unchanged).
- OtOpcUaNodeManager.HistoryReadAtTime passes the node's scalar DataType
  (AtTimeValueType: built-in type -> TypeCode; arrays/other types => null);
  Raw and UNS NodeIds alike.
- GatewayAtTimeReader converts each raw row to the hinted kind BEFORE the shared
  AtTimeEvaluator runs (Boolean = value != 0 => stepped; integers => Int64 =>
  interpolated, rounded half away from zero, returned as the node's integer
  type; floats Double), so the evaluator's own type branch decides.
- AtTimeEvaluator boxed every interpolated Int64 as a Double (`cond ? (long)x :
  v` widens to double); its "keeping its type" test passed because Shouldly
  ShouldBe compares numbers across types. Fixed (affects SqlServer/QuestDB too)
  and pinned with ShouldBeOfType.

src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/Historian/IHistorianDataSource.cs

@@ -81,6 +81,31 @@ public interface IHistorianDataSource : IDisposable
         IReadOnlyList<DateTime> timestampsUtc,
         CancellationToken cancellationToken);
 
+    /// <summary>
+    ///     Gitea #693: <see cref="ReadAtTimeAsync(string, IReadOnlyList{DateTime}, CancellationToken)"/> with the value type of
+    ///     the node being read, for a backend whose stored values do not carry their type (the Gateway: AVEVA stores every
+    ///     historized type as a numeric analog, so a Boolean comes back as a 0/1 Double). Such a backend uses the hint to apply
+    ///     the AtTime rules exactly as the typed backends do — a Boolean (or String / DateTime) node is stepped, an integer node
+    ///     is interpolated, rounded half away from zero and returned as the node's integer type, a floating-point node is
+    ///     interpolated. A backend that stores typed values ignores it: the default forwards to the hint-less overload, so
+    ///     SqlServer, QuestDB and the Null source need no change.
+    /// </summary>
+    /// <param name="fullReference">The full reference of the tag to read.</param>
+    /// <param name="timestampsUtc">The list of timestamps to read values at.</param>
+    /// <param name="valueType">
+    ///     The scalar value type of the node (<see cref="TypeCode.Boolean"/>, the integer codes, <see cref="TypeCode.Single"/>,
+    ///     <see cref="TypeCode.Double"/>, <see cref="TypeCode.String"/>, <see cref="TypeCode.DateTime"/>), or <c>null</c> when
+    ///     unknown, not scalar, or not one of those — the backend's own policy then applies.
+    /// </param>
+    /// <param name="cancellationToken">A cancellation token that can be used to cancel the operation.</param>
+    /// <returns>One sample per requested timestamp, in the same order as <paramref name="timestampsUtc"/>.</returns>
+    Task<HistoryReadResult> ReadAtTimeAsync(
+        string fullReference,
+        IReadOnlyList<DateTime> timestampsUtc,
+        TypeCode? valueType,
+        CancellationToken cancellationToken) =>
+        ReadAtTimeAsync(fullReference, timestampsUtc, cancellationToken);
+
     /// <summary>
     ///     Read historical alarm / event records — OPC UA HistoryReadEvents service.
     ///     Distinct from any live event stream; sources here come from the historian's
@@ -95,7 +120,7 @@ public interface IHistorianDataSource : IDisposable
     ///     <c>uint maxValuesPerNode</c> because their OPC UA HistoryRead surface has no
     ///     equivalent "use default" sentinel.
     ///
-    ///     This surface declares <see cref="ReadAtTimeAsync"/> and <see cref="ReadEventsAsync(string?, DateTime, DateTime, int, CancellationToken)"/>
+    ///     This surface declares <see cref="ReadAtTimeAsync(string, IReadOnlyList{DateTime}, CancellationToken)"/> and <see cref="ReadEventsAsync(string?, DateTime, DateTime, int, CancellationToken)"/>
     ///     as required members — a server-side historian owns the full read surface.
     /// </remarks>
     /// <param name="sourceName">The source name to filter events, or null to return events from all sources.</param>