[iOS] Rive animation sound stops after app backgrounding and switching to another audio app

[AlexisArcs]

Description

<-- When using rive_native in a Flutter application on iOS, the animation audio stops playing after the app goes to the background and another app that uses audio (e.g., YouTube) is opened.
Upon returning to the Flutter app, the Rive animation no longer produces sound.
Sometimes the bug requires exiting and re-entering the app multiple times before it occurs again. -->

Steps To Reproduce

Steps to reproduce the behavior:

1. Run the reproduction project: https://github.com/AlexisArcs/rive_bug_reproduction
2. Start the app and play the Rive animation with sound.
3. Put the app in the background.
4. Open another app that uses audio (e.g., YouTube or Spotify).
5. Return to the Flutter app.
6. Observe that the animation no longer plays sound.
7. (Optional) Repeat steps 3–5 multiple times — sometimes it requires two or more cycles for the bug to reappear.

Expected behavior

<-- When returning to the app after it was in the background, Rive animations should continue to play sound normally, without requiring a restart or multiple app switches.-->

Device & Versions (please complete the following information)

• Device: Physical iOS devices
  • iPhone 12 (iOS 18.5)
  • iPhone 12 Pro Max (iOS 18.6.2)
• Flutter Version:

Flutter 3.35.3 • channel stable • https://github.com/flutter/flutter.git
Framework • revision a402d9a437 (il y a 7 semaines) • 2025-09-03 14:54:31 -0700
Engine • hash 672c59cfa87c8070c20ba2cd1a6c2a1baf5cf08b (revision ddf47dd3ff) (1 months ago) • 2025-09-03 20:02:13.000Z
Tools • Dart 3.9.2 • DevTools 2.48.0