ANR may occur when used with apps that provide document providers

[masiroyuki]

Describe the bug
ANR may occur when accessing applications that provide network folders

To Reproduce

1. install CIFS Documents Provider to use SMB

2. Connect to SMB server with CIFS Documents Provider

3. Open the demo application and get permission to access uri

4. Turn off wifi (but leave LTE on)

5. Execute canRead or exists

6. UI freezes and ANR occurs

Expected behavior
By separating threads in a coroutine
Prevents the UI from freezing

Screenshots

demomp4.mp4

Desktop (please complete the following information):

• OS: Windows11 pro
• Browser Edge
• Version latest

Smartphone (please complete the following information):

• Device: pixel6a
• OS: Android13
• Browser Edge
• Version latest

Additional context

DemoApp

import 'package:flutter/material.dart';
import 'package:shared_storage/shared_storage.dart' as saf;

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
        useMaterial3: true,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key, required this.title});

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

  Uri? selectUri;

  String answer = '';

  void openDocumentTree() => saf.openDocumentTree().then((value) {
    setState(() {
      selectUri = value;
    });
  });

  void canRead(Uri? uri) => saf.canRead(uri ?? Uri()).then((value) {
    setState(() {
      answer = value.toString();
    });
  });

  void exists(Uri? uri) => saf.exists(uri ?? Uri()).then((value) {
    setState(() {
      answer = value.toString();
    });
  });
  

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(

        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'uri: ${selectUri.toString()}',
              style: Theme.of(context).textTheme.headlineLarge,
            ),
            Text(
              'answer: $answer',
              style: Theme.of(context).textTheme.headlineLarge,
            ),
            const SizedBox(height: 200,),
             FilledButton(
              onPressed: () => openDocumentTree(),
              child: Text('openDocumentTree',
              style: Theme.of(context).textTheme.bodyMedium,)),
            FilledButton(
              onPressed: () => canRead(selectUri),
              child: Text('canRead',
              style: Theme.of(context).textTheme.bodyMedium,)),
            FilledButton(
              onPressed: () => exists(selectUri),
              child: Text('exists',
              style: Theme.of(context).textTheme.bodyMedium,))
          ],
        ),
      ),
    );
  }
}