fix(Android, Tabs): clean up stale fragments instead of crashing

[jpancotti]

When the FragmentManager has stale fragments from a previous tabs session (e.g., after login → tabs → logout → login → tabs flow), the app would crash with "[RNScreens] There can be only a single focused tab". This fix gracefully cleans up stale fragments instead of crashing.

Description

When using NativeTabs with navigation flows that mount/unmount the tab container (e.g., auth flows), the native Android FragmentManager may retain fragments from a previous session. The previous assertion would crash the app; this fix removes stale fragments gracefully.

Fixes apps using expo-router NativeTabs with conditional rendering based on auth state.

Changes

• Replaced crash assertion with defensive cleanup in TabsHost.kt
• When multiple fragments exist, removes extras via commitNowAllowingStateLoss()
• Logs cleanup for debugging via RNSLog.d

Test code and steps to reproduce

function RootLayout() {
  const { isLoggedIn } = useAuth();
  
  if (!isLoggedIn) {
    return <LoginScreen />;
  }
  
  return (
    <Tabs>
      <Tabs.Screen name="home" />
      <Tabs.Screen name="profile" />
    </Tabs>
  );
}

1. Login → see tabs
2. Logout → see login screen
3. Login again
4. Before: Crash with "There can be only a single focused tab"
5. After: Tabs work correctly, stale fragments cleaned up

Checklist

• Included code example that can be used to test this change
• Updated TS types
• Updated documentation:
  • https://github.com/software-mansion/react-native-screens/blob/main/guides/GUIDE_FOR_LIBRARY_AUTHORS.md
  • https://github.com/software-mansion/react-native-screens/blob/main/native-stack/README.md
  • https://github.com/software-mansion/react-native-screens/blob/main/src/types.tsx
  • https://github.com/software-mansion/react-native-screens/blob/main/src/native-stack/types.tsx
• Ensured that CI passes