refactor(virtualtags): retire dormant VirtualTagEngine/Source/Definition + TimerTriggerScheduler (#603)

TimerTriggerScheduler was welded to the engine and has no production consumer.

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe

src/Core/ZB.MOM.WW.OtOpcUa.Commons/Engines/IVirtualTagEvaluator.cs

@@ -5,8 +5,7 @@ namespace ZB.MOM.WW.OtOpcUa.Commons.Engines;
 /// <summary>
 ///     Abstraction over the compiled virtual-tag expression engine. Runtime consumes this so
 ///     <see cref="VirtualTagActor"/> can stay free of Roslyn / scripting machinery and the
-///     production wiring binds an adapter over <c>VirtualTagEngine</c> from
-///     <c>Core.VirtualTags</c>.
+///     production wiring binds <c>RoslynVirtualTagEvaluator</c> (Host).
 /// </summary>
 public interface IVirtualTagEvaluator
 {
@@ -98,7 +97,7 @@ public static class ScriptEvalFailureReasons
 }
 
 /// <summary>Returns <see cref="VirtualTagEvalResult.NoChange"/> from every call. Bound by default
-/// when the production <c>VirtualTagEngine</c> adapter hasn't been registered (Mac dev, tests).</summary>
+/// when the production <c>RoslynVirtualTagEvaluator</c> hasn't been registered (Mac dev, tests).</summary>
 public sealed class NullVirtualTagEvaluator : IVirtualTagEvaluator
 {
     public static readonly NullVirtualTagEvaluator Instance = new();