Make all reactor script invocations thread safe

Might be a bit overkill to force synchronization
for every single method invocation when the only
scheduling done in reactor scripts are:
- 5511000 (summon Targa)
- 5511001 (summon Scarlion)

src/main/java/scripting/SynchronizedInvocable.java

@@ -13,10 +13,14 @@ import javax.script.ScriptException;
 public class SynchronizedInvocable implements Invocable {
     private final Invocable invocable;
 
-    public SynchronizedInvocable(Invocable invocable) {
+    private SynchronizedInvocable(Invocable invocable) {
         this.invocable = invocable;
     }
 
+    public static Invocable of(Invocable invocable) {
+        return new SynchronizedInvocable(invocable);
+    }
+
     @Override
     public synchronized Object invokeMethod(Object thiz, String name, Object... args) throws ScriptException, NoSuchMethodException {
         return invocable.invokeMethod(thiz, name, args);