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/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests/ModbusDriverProbeParityTests.cs

@@ -51,6 +51,6 @@ public sealed class ModbusDriverProbeParityTests
         var (target, error) = ModbusDriverProbe.TryParseProbeTarget(
             "not valid json {{", fallbackTimeout: TimeSpan.FromSeconds(5));
         target.ShouldBeNull();
-        error.ShouldContain("invalid");
+        error.ShouldNotBeNull().ShouldContain("invalid");
     }
 }

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests/ModbusDriverProbeTests.cs

@@ -181,7 +181,7 @@ public sealed class ModbusDriverProbeTests
         var result = await _probe.ProbeAsync(Config(port), QuickTimeout, CancellationToken.None);
 
         // The server task should have completed (or close enough).
-        await serverTask.WaitAsync(TimeSpan.FromSeconds(2), TestContext.Current.CancellationToken).ConfigureAwait(false);
+        await serverTask.WaitAsync(TimeSpan.FromSeconds(2), TestContext.Current.CancellationToken);
 
         result.Ok.ShouldBeFalse();
         result.Message.ShouldNotBeNull();
@@ -211,7 +211,7 @@ public sealed class ModbusDriverProbeTests
 
         var result = await _probe.ProbeAsync(Config(port), QuickTimeout, CancellationToken.None);
 
-        await serverTask.WaitAsync(TimeSpan.FromSeconds(3), TestContext.Current.CancellationToken).ConfigureAwait(false);
+        await serverTask.WaitAsync(TimeSpan.FromSeconds(3), TestContext.Current.CancellationToken);
 
         result.Ok.ShouldBeTrue();
         result.Message.ShouldBe("Modbus FC03 OK");
@@ -241,7 +241,7 @@ public sealed class ModbusDriverProbeTests
 
         var result = await _probe.ProbeAsync(Config(port), QuickTimeout, CancellationToken.None);
 
-        await serverTask.WaitAsync(TimeSpan.FromSeconds(3), TestContext.Current.CancellationToken).ConfigureAwait(false);
+        await serverTask.WaitAsync(TimeSpan.FromSeconds(3), TestContext.Current.CancellationToken);
 
         result.Ok.ShouldBeTrue();
         result.Message.ShouldNotBeNull();

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests/ModbusLifecycleHygieneTests.cs

@@ -497,8 +497,8 @@ public sealed class ModbusLifecycleHygieneTests(ITestOutputHelper output)
         });
 
         await Task.WhenAll(
-            Task.Run(() => drv.InitializeAsync("{}", CancellationToken.None)),
-            Task.Run(() => drv.InitializeAsync("{}", CancellationToken.None)));
+            Task.Run(() => drv.InitializeAsync("{}", CancellationToken.None), TestContext.Current.CancellationToken),
+            Task.Run(() => drv.InitializeAsync("{}", CancellationToken.None), TestContext.Current.CancellationToken));
 
         var built = handed.ToArray();
         built.Length.ShouldBe(2);