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.Scripting.Tests/CompiledScriptCacheTests.cs

@@ -13,11 +13,6 @@ namespace ZB.MOM.WW.OtOpcUa.Core.Scripting.Tests;
 [Trait("Category", "Unit")]
 public sealed class CompiledScriptCacheTests
 {
-    private sealed class CompileCountingGate
-    {
-        public int Count;
-    }
-
     /// <summary>Verifies that the first call to GetOrCompile compiles the script and caches the evaluator.</summary>
     [Fact]
     public void First_call_compiles_and_caches()
@@ -112,7 +107,7 @@ public sealed class CompiledScriptCacheTests
 
     /// <summary>Verifies that concurrent compiles of the same source deduplicate to a single compilation.</summary>
     [Fact]
-    public void Concurrent_compiles_of_the_same_source_deduplicate()
+    public async Task Concurrent_compiles_of_the_same_source_deduplicate()
     {
         // LazyThreadSafetyMode.ExecutionAndPublication guarantees only one compile
         // even when multiple threads race GetOrCompile against an empty cache.
@@ -122,13 +117,13 @@ public sealed class CompiledScriptCacheTests
         const string src = """return 99;""";
 
         var tasks = Enumerable.Range(0, 20)
-            .Select(_ => Task.Run(() => cache.GetOrCompile(src)))
+            .Select(_ => Task.Run(() => cache.GetOrCompile(src), TestContext.Current.CancellationToken))
             .ToArray();
-        Task.WhenAll(tasks).GetAwaiter().GetResult();
+        var evaluators = await Task.WhenAll(tasks);
 
-        var firstInstance = tasks[0].Result;
-        foreach (var t in tasks)
-            ReferenceEquals(t.Result, firstInstance).ShouldBeTrue();
+        var firstInstance = evaluators[0];
+        foreach (var e in evaluators)
+            ReferenceEquals(e, firstInstance).ShouldBeTrue();
         cache.Count.ShouldBe(1);
     }