fix(historian): page by the backend's timestamp resolution; QuestDB AtTime stamps the requested time

IHistorianDataSource.TimestampResolutionTicks (default 1; QuestDB 10). A drained tie
cluster now steps off T by the resolution, so a forward one-value-per-page read on a
microsecond backend no longer re-reads the same sample forever (C1). QuestDB AtTime
results carry the client's original request time (M3); regression for the NEXT seek
skipping a tombstone (M1). Conformance backend wires the real writer and updater.

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe

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

@@ -107,4 +107,19 @@ public interface IHistorianDataSource : IDisposable
     /// </summary>
     /// <returns>The current health snapshot for the historian backend.</returns>
     HistorianHealthSnapshot GetHealthSnapshot();
+
+    /// <summary>
+    ///     The backend's storage timestamp resolution, in <see cref="DateTime"/> ticks (100 ns): the smallest step
+    ///     between two distinct stored timestamps. <c>1</c> (the default) means full tick precision; QuestDB stores
+    ///     microseconds and reports <c>10</c>.
+    /// </summary>
+    /// <remarks>
+    ///     The server's HistoryRead-Raw paging steps OFF a drained timestamp by this amount (forward
+    ///     <c>T + resolution</c>, reverse <c>T − resolution</c>). Stepping by less than the resolution is not
+    ///     progress on a backend that truncates its inputs: <c>T + 1 tick</c> is truncated back to <c>T</c>, the
+    ///     same sample comes back, and a one-value-per-page forward read loops forever. Stepping by the resolution is
+    ///     still lossless, because no stored timestamp can lie strictly between <c>T</c> and <c>T ± resolution</c>.
+    ///     Same-timestamp ties are unaffected (they are paged within the timestamp, never stepped over).
+    /// </remarks>
+    long TimestampResolutionTicks => 1;
 }