Ensure widgets always get a single callback (#7579)

The other side of reactivity. Ensure that vue mode always registers a
callback on litegraph nodes and never registers more than one.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7579-Ensure-widgets-always-get-a-single-callback-2cc6d73d365081e2a488c38ae394efc0)
by [Unito](https://www.unito.io)

src/lib/litegraph/src/types/widgets.ts

@@ -284,6 +284,7 @@ export interface IBaseWidget<
   /** Widget type (see {@link TWidgetType}) */
   type: TType
   value?: TValue
+  vueTrack?: () => void
 
   /**
    * Whether the widget value should be serialized on node serialization.