Update import path for createSharedState in demo app

Replaced the local `createSharedState` import with the one from the `react-shared-states` package to ensure the demo app reflects the library's intended usage.

- Simplifies and aligns the demo app with the external library usage.

Author: HichemTab-tech

demo/app.tsx

@@ -10,7 +10,7 @@ import {
 import './FakeSharedEmitter';
 import {FakeSharedEmitter} from "./FakeSharedEmitter";
 import {useEffect, useState} from "react";
-import {createSharedState} from "../src/hooks/use-shared-state";
+import {createSharedState} from "react-shared-states";
 
 FakeSharedEmitter.intervalDuration = 3000;
 window.sharedSubscriptionsApi = sharedSubscriptionsApi;