fix: middlewares wont work with dynamic routes

[renancaraujo]

Description

Middlewares inside dynamic routes are not recognized.

Steps To Reproduce

1. Create a frog server with the following route structure

routes/
  - _middleware.dart
  - [id]/
    - index.dart
    - _middleware.dart

2. On the root middleware, put the following content:

import 'package:dart_frog/dart_frog.dart';

Handler middleware(Handler handler) {
  return handler
      .use(provider<String>((context) {
    return 'root middleware haha';
  }));
}

3. On the middleware under /[id], put the following content:

import 'package:dart_frog/dart_frog.dart';

Handler middleware(Handler handler) {
  return handler
      .use(provider<String>((context) {
    return 'id middleware hihi';
  }));
}

4. On /[id]/index.dart put the following content:

import 'package:dart_frog/dart_frog.dart';

Response onRequest(RequestContext context) {
  final thingy = context.read<String>();
  return Response(body: 'result: $thingy');
}

5. Start the server and go to http://localhost:8080/someid
6. See the result: result: root middleware haha

Expected Behavior

The handler at /[id]/index.dart should; receive a context with information for the closest middleware, not the root one.

Additional Context

Reproducible with the CLI version 0.0.2-dev.7

[felangel]

related to dart-lang/shelf#250 and google/dart-neats#40

[BeatriceMitchell]

Descoping from 0.1, moving to 1.0