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/Client/ZB.MOM.WW.OtOpcUa.Client.Shared.Tests/OpcUaClientServiceTests.cs

@@ -860,7 +860,6 @@ public class OpcUaClientServiceTests : IDisposable
     [Fact]
     public async Task GetRedundancyInfoAsync_MissingOptionalArrays_ReturnsGracefully()
     {
-        var readCallIndex = 0;
         var session = new FakeSessionAdapter
         {
             ReadResponseFunc = nodeId =>
@@ -1554,7 +1553,7 @@ public class OpcUaClientServiceTests : IDisposable
             {
                 await _service.SubscribeAsync(nodeId);
                 await _service.UnsubscribeAsync(nodeId);
-            }));
+            }, TestContext.Current.CancellationToken));
         }
 
         // No InvalidOperationException from concurrent Dictionary mutation.
@@ -1634,7 +1633,6 @@ public class OpcUaClientServiceTests : IDisposable
         var alarmFakeSub = new FakeSubscriptionAdapter();
 
         // First CreateSubscription call → data subscription; second → alarm subscription.
-        var callIndex = 0;
         var session = new FakeSessionAdapter
         {
             NextSubscription = dataFakeSub