fix(historian): QuestDB modified reads keep a landed change whose marker was lost; H2 review NITs (lmxopcua#778)

QuestDB modified-history reads dropped every still-pending trail row that was
not the latest at its source time, so V0->V1 (applied marker never written)
followed by V1->V2 hid the V0->V1 change for good. A pending row below the
latest is now served when the NEXT trail row at that time recorded a different
prior value (kind, value, status or the prior's server_ts) - the next change saw
what this one wrote; an orphan of a change that never landed leaves the same
prior for the next row and stays hidden. QuestDB window functions reject
VARCHAR, so the next row's prior comes from a LEFT JOIN on (ts, lead(id)).
The updater's comment and marker-failure log no longer claim modified reads
"still serve it" unconditionally.

Regression tests (QuestDB 10.0.1 throwaway container): marker lost then a
replace / delete at the same time; an orphan followed by a marker-lost retry
then a later change (orphan still dropped); the random marker-mix fuzz now
varies the recorded priors. All four fail on the old filter.

NITs:
- SqlServerHistorianValueWriter: a SqlException raised while the token is
  cancelled (SqlClient's "Operation cancelled by user") is rethrown as
  OperationCanceledException instead of booked as a failed write. Integration
  test holds a TABLOCKX on Sample and cancels mid-INSERT; it returned false before.
- SqlServerHistorianDataUpdater.DeleteRawBatches is an Interlocked counter.
- HistoryReadEvents: an event filter whose SDK validation throws (unknown
  operator) failed with the generic BadUnexpectedError; the node manager now
  re-throws any failed event-filter validation as BadEventFilterInvalid.

Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.SqlServer/SqlServerHistorianValueWriter.cs

@@ -95,6 +95,12 @@ internal sealed class SqlServerHistorianValueWriter : IHistorianValueWriter
         {
             throw; // the drain pass was cancelled (shutdown) — not a write failure of this tag
         }
+        catch (SqlException ex) when (ct.IsCancellationRequested)
+        {
+            // SqlClient reports a command cancelled mid-flight as a SqlException ("Operation cancelled by user"), not an
+            // OperationCanceledException: still the drain pass's cancellation, never a write failure of this tag.
+            throw new OperationCanceledException("The SQL historian live-value write was cancelled.", ex, ct);
+        }
         catch (Exception ex)
         {
             _log.LogWarning("SQL historian live-value write failed ({Exception}); will retry.", ex.GetType().Name);