[BUG] Always loading for multipart request

[paulmwk]

Describe the bug
If the request is a multipart request, it will constantly load in Alice.
Because in dart http package, the content-type header will be set to a new value with a random boundary after request interceptors.

The original request header is different from response.base.request!.headers.
Alice cannot match request and response, and it will constantly load.

https://github.com/dart-lang/http/blob/master/pkgs/http/lib/src/multipart_request.dart#L87

Below is response.base.request!.headers

{alice_token: 1704769019807, content-type: multipart/form-data; boundary=dart-http-boundary-AsZ9bc8Ke2mL_zsSENWVPk4wA3TvawN2LwJdX57EOMEh7YyHY1R}

To Reproduce

1. create a Flutter application called demo_app
2. install chopper, chopper_generator, http, http_parser and build_runner
3. click the call API button
4. request will constantly load

example_service.dart

@ChopperApi(baseUrl: '/')
abstract class ExampleService extends ChopperService {
  // A helper method that helps instantiating the service. You can omit this method and use the generated class directly instead.
  static ExampleService create([ChopperClient? client]) =>
      _$ExampleService(client);

  @Post(path: 'upload')
  @Multipart()
  Future<Response> postExample(
      {@PartFile('file') required MultipartFile files});
}

main.dart

import 'dart:async';

import 'package:alice/alice.dart';
import 'package:chopper/chopper.dart';
import 'package:demo_app/example_service.dart';
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;

final GlobalKey<NavigatorState> navigatorKey = GlobalKey();

final alice = Alice(navigatorKey: navigatorKey, showNotification: false);

final chopper = ChopperClient(
  baseUrl: Uri.parse('https://example.com'),
  services: [
    ExampleService.create(),
  ],
  interceptors: [
    alice.getChopperInterceptor(),
  ],
);

void main() async {

  WidgetsFlutterBinding.ensureInitialized();
  // Run app.
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) => MaterialApp(
        navigatorKey: navigatorKey,
        home: const MyHomePage(),
      );
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key});

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

class _MyHomePageState extends State<MyHomePage> {
  @override
  void initState() {
    super.initState();
  }

  Future<void> callApi() async {
    final response = await chopper
        .getService<ExampleService>()
        .postExample(files: http.MultipartFile.fromString('img', '123'));
    print(response.base.request!.headers);
  }

  @override
  Widget build(BuildContext context) => Scaffold(
        appBar: AppBar(
          title: const Text('Demo'),
        ),
        body: SingleChildScrollView(
          child: Center(
            child: Column(
              children: [
                ElevatedButton(
                  onPressed: alice.showInspector,
                  child: const Text('Open Alice'),
                ),
                ElevatedButton(
                  onPressed: callApi,
                  child: const Text('Call API'),
                ),
              ],
            ),
          ),
        ),
      );
}

Expected behavior
Multipart request should not load constantly.
Response should be able to match the request using the getRequestHashCode method.

Additional context
NA

Alice Version
0.4.1