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.

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Sql.Common.Tests/AtTimeEvaluatorTests.cs

@@ -83,6 +83,11 @@ public sealed class AtTimeEvaluatorTests
         var n = S(10, HistorianValue.FromInt64(15), Good);
         AtTimeEvaluator.Evaluate(At(5), p, n, Now, Now).Value.ShouldBe(13L); // 12.5 ⇒ 13
         AtTimeEvaluator.Evaluate(At(2), p, n, Now, Now).Value.ShouldBe(11L);
+        // #693: ShouldBe compares numbers across types, so the type needs its own assertion — a C# conditional
+        // `long : double` boxed a Double here, and the line above still passed.
+        AtTimeEvaluator.Evaluate(At(5), p, n, Now, Now).Value.ShouldBeOfType<long>();
+        AtTimeEvaluator.Evaluate(At(5), S(0, HistorianValue.FromDouble(10), Good), S(10, HistorianValue.FromDouble(15), Good), Now, Now)
+            .Value.ShouldBeOfType<double>();
     }
 
     [Fact]