fix(scripted-alarms): resolve Medium code-review finding (Core.ScriptedAlarms-012)

Add engine-level tests covering the six gaps identified in the finding:
(1) timed-shelve auto-expiry driven via injectable clock + RunShelvingCheckForTest
    hook so timer tests are deterministic;
(2) ConfirmAsync, TimedShelveAsync/UnshelveAsync round-trip, EnableAsync engine
    methods exercised end-to-end;
(3) OnEvent subscriber-throws isolation — engine state advances and stays
    operational after a subscriber throws;
(4) IAlarmStateStore.SaveAsync failure leaves in-memory state unchanged (locks in
    the persist-before-update invariant from finding-007);
(5) second LoadAsync does not leak the old timer (regression for finding-002);
(6) AreInputsReady cold-start guard correctly blocks on Bad/missing inputs and
    allows Uncertain-quality inputs through.

Expose RunShelvingCheckForTest() internal method on ScriptedAlarmEngine to
support deterministic timer tests.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/Core/ZB.MOM.WW.OtOpcUa.Core.ScriptedAlarms/ScriptedAlarmEngine.cs

@@ -407,6 +407,13 @@ public sealed class ScriptedAlarmEngine : IDisposable
         _ = ShelvingCheckAsync(ids, CancellationToken.None);
     }
 
+    /// <summary>
+    ///     Test hook — triggers a shelving check synchronously without waiting for
+    ///     the 5-second timer. Allows tests that inject a controllable clock to advance
+    ///     time and immediately drive timed-shelve expiry. (Core.ScriptedAlarms-012)
+    /// </summary>
+    internal void RunShelvingCheckForTest() => RunShelvingCheck();
+
     private async Task ShelvingCheckAsync(IReadOnlyList<string> alarmIds, CancellationToken ct)
     {
         try