fix(vtags): real script timeout + ALC-safe compile cache (arch-review 02/U2,U3)

U2 (Critical): RoslynVirtualTagEvaluator ran scripts with a CancellationToken
that a synchronous Roslyn script can never observe, so one CPU-bound/infinite-
loop virtual-tag script hung the owning VirtualTagActor forever (no timeout, no
recovery). Route evaluation through the existing TimedScriptEvaluator (Task.Run
+ WaitAsync) so the wall-clock budget is real; a runaway script now returns Bad
within the timeout instead of wedging the actor.

U3 (High): the live path cached evaluators in a raw ConcurrentDictionary never
cleared on republish, leaking a collectible AssemblyLoadContext per edited
script forever. Swap in the purpose-built CompiledScriptCache (Lazy single-
compile, dispose-on-Clear) and add an apply-boundary clear: a new narrow
IScriptCacheOwner seam the VirtualTagHostActor calls on each ApplyVirtualTags
generation (mirrors ScriptedAlarmEngine's per-generation clear).

Tests: infinite-loop-fails-within-timeout (bounded by WaitAsync so a regression
fails instead of hanging), happy-path-after-wrapping, ClearCompiledScripts-
empties-cache, and a host-actor wiring guard asserting each apply generation
calls ClearCompiledScripts (theme #1 production-caller assertion). Host.Integration
VT suite 18/18, Runtime VT suite 12/12.

src/Server/ZB.MOM.WW.OtOpcUa.Runtime/VirtualTags/VirtualTagHostActor.cs

@@ -85,6 +85,12 @@ public sealed class VirtualTagHostActor : ReceiveActor
 
     private void OnApply(ApplyVirtualTags msg)
     {
+        // Apply-boundary compile-cache drop: each deploy generation may carry edited script sources, and
+        // the production evaluator roots one collectible AssemblyLoadContext per compiled expression. Drop
+        // them here (mirroring ScriptedAlarmEngine's per-generation clear) so stale ALCs are reclaimed
+        // instead of accreting across edits. No-op for evaluators without a cache (NullVirtualTagEvaluator).
+        (_evaluator as IScriptCacheOwner)?.ClearCompiledScripts();
+
         var desired = new HashSet<string>(msg.Plans.Select(p => p.VirtualTagId), StringComparer.Ordinal);
 
         // Stop + forget children whose vtagId is no longer desired. Stopping the child triggers its