fix: Set the history state to null

As recommended in the Next.js docs for shallow routing.

Historically, while Next.js didn't support shallow routing (<14.1.0),
maintaining the history state was the way to keep
the app router state.

packages/nuqs/src/update-queue.ts

@@ -182,7 +182,7 @@ function flushUpdateQueue(router: Router): [URLSearchParams, null | unknown] {
         options.history === 'push' ? history.pushState : history.replaceState
       updateMethod.call(
         history,
-        history.state,
+        null,
         // Our own updates have a marker to prevent syncing
         // when the URL changes (we've already sync'd them up
         // via `emitter.emit(key, newValue)` above, without