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/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/CalculationTimerScheduler.cs

@@ -3,12 +3,10 @@ using Microsoft.Extensions.Logging;
 namespace ZB.MOM.WW.OtOpcUa.Driver.Calculation;
 
 /// <summary>
-///     Periodic re-evaluation scheduler for calc tags carrying a <c>timerIntervalMs</c>. A deliberate
-///     mirror of the VirtualTag <c>TimerTriggerScheduler</c> (<c>Core.VirtualTags</c>): one
+///     Periodic re-evaluation scheduler for calc tags carrying a <c>timerIntervalMs</c>. One
 ///     <see cref="System.Threading.Timer"/> per distinct interval group (so the wire count stays low
 ///     regardless of tag count) with a per-group in-flight flag that skips a tick when the prior tick for
-///     the same group is still running. Revived <b>inside the driver</b> because the VT scheduler is welded
-///     to <c>VirtualTagEngine.EvaluateOneAsync</c>; here each tick invokes the driver's own evaluate
+///     the same group is still running. Each tick invokes the driver's own evaluate
 ///     callback per tag in the group.
 /// </summary>
 internal sealed class CalculationTimerScheduler : IDisposable