Auto: focas-f3a — cnc_rdalmhistry alarm-history extension

Adds FocasAlarmProjection with two modes (ActiveOnly default, ActivePlusHistory)
that polls cnc_rdalmhistry on connect + on a configurable cadence (5 min default,
HistoryDepth=100 capped at 250). Emits historic events via IAlarmSource with
SourceTimestampUtc set from the CNC's reported timestamp; dedup keyed on
(OccurrenceTime, AlarmNumber, AlarmType). Ships the ODBALMHIS packed-buffer
decoder + encoder in Wire/FocasAlarmHistoryDecoder.cs and threads
ReadAlarmHistoryAsync through IFocasClient (default no-op so existing transport
variants stay back-compat). FocasDriver now implements IAlarmSource.

13 new unit tests cover: mode switch, dedup, distinct-timestamp emission,
type-as-key behaviour, OccurrenceTime passthrough (not Now), HistoryDepth
clamp/fallback, and decoder round-trip. All 341 FOCAS unit tests still pass.

Docs: docs/drivers/FOCAS.md (new), docs/v2/focas-deployment.md (new),
docs/v2/implementation/focas-wire-protocol.md (new),
docs/v2/implementation/focas-simulator-plan.md (new),
docs/drivers/FOCAS-Test-Fixture.md (alarm-history bullet appended).

Closes #267

tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/FakeFocasClient.cs

@@ -107,6 +107,29 @@ internal class FakeFocasClient : IFocasClient
         return Task.FromResult<(byte[]?, uint)>((buf, FocasStatusMapper.Good));
     }
 
+    /// <summary>
+    ///     Canned alarm-history payload returned to <see cref="ReadAlarmHistoryAsync"/>.
+    ///     Defaults to empty so tests that don't care about history get the back-compat
+    ///     no-op behaviour. Tests asserting <c>cnc_rdalmhistry</c> behaviour seed entries
+    ///     here (issue #267, plan PR F3-a).
+    /// </summary>
+    public List<FocasAlarmHistoryEntry> AlarmHistory { get; } = new();
+
+    /// <summary>
+    ///     Ordered log of <c>cnc_rdalmhistry</c>-shaped calls observed on this fake session
+    ///     (depth-per-call). Tests assert this length to verify the projection's poll
+    ///     cadence + that <c>HistoryDepth</c> got clamped to the wire correctly.
+    /// </summary>
+    public List<int> AlarmHistoryReadLog { get; } = new();
+
+    public virtual Task<IReadOnlyList<FocasAlarmHistoryEntry>> ReadAlarmHistoryAsync(
+        int depth, CancellationToken ct)
+    {
+        AlarmHistoryReadLog.Add(depth);
+        IReadOnlyList<FocasAlarmHistoryEntry> snap = AlarmHistory.ToList();
+        return Task.FromResult(snap);
+    }
+
     public virtual void Dispose()
     {
         DisposeCount++;