fix: Add feature to control systemic property of executeCode

engine/updategraph/src/main/java/io/deephaven/engine/util/systemicmarking/SystemicObjectTracker.java

@@ -34,14 +34,24 @@ public static boolean isSystemicThread() {
     }
 
     /**
-     * Marks the current thread as systemically important, this is a permanent change.
+     * Marks the current thread as systemically important, this can be changed with {@link #markThreadNotSystemic()}.
      */
     public static void markThreadSystemic() {
         if (SYSTEMIC_OBJECT_MARKING_ENABLED) {
             SYSTEMIC_CREATION_THREAD.set(true);
         }
     }
 
+    /**
+     * Marks the current thread as not systemically important, this can be changed with {@link #markThreadSystemic()}
+     * ()}
+     */
+    public static void markThreadNotSystemic() {
+        if (SYSTEMIC_OBJECT_MARKING_ENABLED) {
+            SYSTEMIC_CREATION_THREAD.set(false);
+        }
+    }
+
     /**
      * Execute the supplier with the thread's systemic importance set to the value of systemicThread.
      *