fix(historian): live-gate 8 F1 — per-sample counts and picks from one table version (#680 follow-up)

QuestDB Start/End/Delta reads of a tag being written intermittently failed
BadHistoryOperationUnsupported (InvalidCastException: Column 'ts_3' is null):
the StartEnd query referenced its CTE four times and QuestDB opens a table
reader per reference, so a row committed between two of them was counted but
not picked. MinimumActualTime/MaximumActualTime had the same race and returned
a value-less Good.

(a) SQL
- QuestDB StartEnd: one scan, one GROUP BY — first()/last() for the
  any-quality picks, arg_min/arg_max keyed on the usable rows' time for the
  usable picks (no str_value: arg_min has no VARCHAR form; only Delta reads
  them). Byte-identical output to the old query on a 1M-row tag, ~15% faster.
- SqlServer StartEnd: one windowed pass + conditional MAX (was five CTE
  references); identical output, 1.4-3x faster.
- ActualTime kept on both backends: every single-scan form measured 1.2-2.4x
  slower; its inconsistency is absorbed by (b).

(b) Defence in depth on both backends
- ReadBucket takes DbDataReader and reads absent picks as null
  (ReadStoredOrNull) instead of throwing.
- AggregateEvaluator: Delta with a missing first/last usable pick and
  ActualTime with a missing extreme are BadNoData (were BadAggregateInvalidInputs
  / a value-less Good); Start/End with no pick already were.
- Unit tests (Sql.Common evaluator, QuestDb + SqlServer mappers over a
  DataTableReader) fail with the guards removed.

LiveWriteReadRaceStressTests (QuestDB integration, opt-in via
HISTORIAN_QUESTDB_STRESS_SECONDS, Category=SlowUnit): single-row writer vs
4 tight-loop readers. Old code: 6 faults in ~105k reads; new: 0 in 106k.

Docs: Historian.md QuestDB processed-read note; F2 (Min/Max on the interval
start: SDK raw, ours Calculated) and F3 (integer tags: SDK casts interpolated
values to the integer type, ours Double) added to the SDK-parity deviations.

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.QuestDb/QuestDbConnection.cs

@@ -201,14 +201,14 @@ internal sealed class QuestDbConnection : IAsyncDisposable, IDisposable
     /// <param name="r">Reader positioned on a row.</param>
     /// <param name="i">Column ordinal.</param>
     /// <returns>The timestamp with <c>Kind=Utc</c>.</returns>
-    public static DateTime ReadUtc(NpgsqlDataReader r, int i) =>
+    public static DateTime ReadUtc(System.Data.Common.DbDataReader r, int i) =>
         DateTime.SpecifyKind(r.GetDateTime(i), DateTimeKind.Utc);
 
     /// <summary>Reads a <c>BYTE</c> column (QuestDB returns <c>smallint</c>); NULL (never stored) reads as 0 (Empty).</summary>
     /// <param name="r">Reader positioned on a row.</param>
     /// <param name="i">Column ordinal.</param>
     /// <returns>The byte value.</returns>
-    public static byte ReadKind(NpgsqlDataReader r, int i) => r.IsDBNull(i) ? (byte)0 : (byte)r.GetInt16(i);
+    public static byte ReadKind(System.Data.Common.DbDataReader r, int i) => r.IsDBNull(i) ? (byte)0 : (byte)r.GetInt16(i);
 
     // ---- error classification --------------------------------------------------------------------------------------