feat(auditlog): site script-side emitters stamp ExecutionId

Move the per-script-execution Guid on ScriptRuntimeContext from
_auditCorrelationId to _executionId, and stamp it into the dedicated
AuditEvent.ExecutionId column on every script-side audit row:

- Sync ApiCall / DbWrite: ExecutionId set; CorrelationId reverts to
  null (a sync one-shot call has no operation lifecycle).
- Cached-call script-side rows (CachedSubmit, immediate-completion
  ApiCallCached + CachedResolve) and NotifySend: ExecutionId set;
  CorrelationId unchanged (per-operation TrackedOperationId /
  NotificationId).

Renames the threaded ctor param/field across ExternalSystemHelper,
DatabaseHelper, AuditingDbConnection and AuditingDbCommand, and threads
the id through NotifyHelper/NotifyTarget. The S&F retry-loop cached rows
(CachedCallLifecycleBridge) are out of scope here.

tests/ScadaLink.SiteRuntime.Tests/Scripts/NotifyHelperTests.cs

@@ -69,7 +69,8 @@ public class NotifyHelperTests : TestKit, IAsyncLifetime, IDisposable
             "Plant.Pump3",
             sourceScript,
             TimeSpan.FromSeconds(3),
-            NullLogger.Instance);
+            NullLogger.Instance,
+            Guid.NewGuid());
     }
 
     [Fact]