publicize container id

invui/src/main/java/xyz/xenondevs/invui/internal/menu/CustomContainerMenu.java

@@ -631,7 +631,15 @@ public WindowEventListener getWindowEvents() {
             throw new IllegalStateException("Window is not set");
         return (WindowEventListener) window;
     }
-
+
+    /**
+     * Gets the container ID (window ID) for the window
+     * @return the container id, or -1 if the window isn't a container
+     */
+    public int getContainerId() {
+        return containerId;
+    }
+
     /**
      * A proxy {@link AbstractContainerMenu} for intercepting carried item change and general bukkit interoperability.
      */

invui/src/main/java/xyz/xenondevs/invui/window/AbstractWindow.java

@@ -703,7 +703,12 @@ public int getServerWindowState() {
     public int getClientWindowState() {
         return clientWindowState;
     }
-
+
+    @Override
+    public int getContainerId() {
+        return menu.getContainerId();
+    }
+
     @Override
     public void handlePong(int id) {
         clientWindowState = id;

invui/src/main/java/xyz/xenondevs/invui/window/Window.java

@@ -301,7 +301,15 @@ default void incrementWindowState() {
      * @param handler The window state change handler to remove
      */
     void removeWindowStateChangeHandler(Consumer<? super Integer> handler);
-
+
+    /**
+     * Gets the container ID (window ID) for the window
+     * @return the container id, or -1 if the window isn't a container
+     */
+    default int getContainerId() {
+        return -1;
+    }
+
     /**
      * A {@link Window} builder.
      *