test: remaining xUnit1051/1031/1030, CS8602/8604, CS0618, CS0219, CS0649, NU1510 fixes (lmxopcua#725)

Awaited deadline oracles get the runner token; sync-over-async tests made async;
nullable child models asserted via ShouldNotBeNull() return values; obsolete SDK
ctors replaced with the telemetry overloads; dead locals/fixture and the redundant
DI PackageReference removed. No suppressions.

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

tests/Core/ZB.MOM.WW.OtOpcUa.Core.ScriptedAlarms.Tests/ScriptedAlarmEngineTests.cs

@@ -739,7 +739,7 @@ public sealed class ScriptedAlarmEngineTests
 
             up.Push("Temp", 150);
 
-            var winner = await Task.WhenAny(ackDone.Task, Task.Delay(TimeSpan.FromSeconds(3)));
+            var winner = await Task.WhenAny(ackDone.Task, Task.Delay(TimeSpan.FromSeconds(3), TestContext.Current.CancellationToken));
             winner.ShouldBe(ackDone.Task,
                 "subscriber re-entering the engine must not deadlock against _evalGate");
             await ackDone.Task; // surface any inner exception
@@ -753,7 +753,7 @@ public sealed class ScriptedAlarmEngineTests
 
     /// <summary>Verifies that OnEvent emission occurs after the evaluation gate is released, so subscribers can re-enter the engine without deadlocking (regression for Core.ScriptedAlarms-003).</summary>
     [Fact]
-    public void OnEvent_emission_happens_outside_evalGate(/* -003 */)
+    public async Task OnEvent_emission_happens_outside_evalGate(/* -003 */)
     {
         // Direct white-box check on the gate-release ordering: AcknowledgeAsync
         // emits the Acknowledged event AFTER releasing the gate. We assert that
@@ -764,8 +764,8 @@ public sealed class ScriptedAlarmEngineTests
         var eng = Build(up, out _);
         try
         {
-            eng.LoadAsync([Alarm("HighTemp", """return (int)ctx.GetTag("Temp").Value > 100;""")],
-                TestContext.Current.CancellationToken).GetAwaiter().GetResult();
+            await eng.LoadAsync([Alarm("HighTemp", """return (int)ctx.GetTag("Temp").Value > 100;""")],
+                TestContext.Current.CancellationToken);
             // Drive to Active so Acknowledge has something to ack.
             up.Push("Temp", 150);
             // Use the same WaitForAsync that other tests use — synchronously
@@ -796,8 +796,7 @@ public sealed class ScriptedAlarmEngineTests
                 }
             };
 
-            eng.AcknowledgeAsync("HighTemp", "alice", null, CancellationToken.None)
-               .GetAwaiter().GetResult();
+            await eng.AcknowledgeAsync("HighTemp", "alice", null, CancellationToken.None);
 
             gateFreeInsideEmission.ShouldBeTrue(
                 "_evalGate must be released before OnEvent fires so subscribers " +
@@ -844,7 +843,7 @@ public sealed class ScriptedAlarmEngineTests
         // Verify Dispose does NOT complete immediately — it should block waiting
         // for the in-flight task. Without the -006 fix Dispose returns straight
         // away and the background reevaluation can outlive the engine.
-        var prematureFinish = await Task.WhenAny(disposeTask, Task.Delay(200));
+        var prematureFinish = await Task.WhenAny(disposeTask, Task.Delay(200, TestContext.Current.CancellationToken));
         prematureFinish.ShouldNotBe(disposeTask,
             "Dispose must block until in-flight background tasks complete");
 
@@ -1749,7 +1748,7 @@ public sealed class ScriptedAlarmEngineTests
         eng.InFlightCountForTest.ShouldBe(1);
 
         var disposeTask = Task.Run(() => eng.Dispose(), TestContext.Current.CancellationToken);
-        var raced = await Task.WhenAny(disposeTask, Task.Delay(300));
+        var raced = await Task.WhenAny(disposeTask, Task.Delay(300, TestContext.Current.CancellationToken));
         raced.ShouldNotBe(disposeTask, "Dispose must not return while registered background work is still running");
 
         gate.SetResult();