docs(example): simplify /count implementation (#115)

Author: felangel

example/routes/count/_middleware.dart

@@ -1,9 +1,7 @@
-import 'dart:developer';
-
 import 'package:dart_frog/dart_frog.dart';
 
-final _counter = Counter('counter', 'a simple request counter');
+int _count = 0;
 
 Handler middleware(Handler handler) {
-  return handler.use(provider<Counter>((_) => _counter));
+  return handler.use(provider<int>((_) => ++_count));
 }

example/routes/count/index.dart

@@ -1,10 +1,8 @@
-import 'dart:developer';
-
 import 'package:dart_frog/dart_frog.dart';
 
 Response onRequest(RequestContext context) {
-  final counter = context.read<Counter>()..value += 1;
+  final count = context.read<int>();
   return Response(
-    body: 'You have requested this route ${counter.value.toInt()} time(s).',
+    body: 'You have requested this route $count time(s).',
   );
 }

example/test/routes/count/_middleware_test.dart

@@ -1,5 +1,3 @@
-import 'dart:developer';
-
 import 'package:dart_frog/dart_frog.dart';
 import 'package:mocktail/mocktail.dart';
 import 'package:test/test.dart';
@@ -10,12 +8,11 @@ class _MockRequestContext extends Mock implements RequestContext {}
 
 void main() {
   group('middleware', () {
-    test('provides count instance', () async {
-      double? count;
+    test('provides incremented count', () async {
+      int? count;
       final handler = middleware(
         (context) {
-          final counter = context.read<Counter>();
-          count = counter.value += 1;
+          count = context.read<int>();
           return Response(body: '');
         },
       );

example/test/routes/count/index_test.dart

@@ -1,4 +1,3 @@
-import 'dart:developer';
 import 'dart:io';
 
 import 'package:dart_frog/dart_frog.dart';
@@ -9,16 +8,12 @@ import '../../../routes/count/index.dart' as route;
 
 class _MockRequestContext extends Mock implements RequestContext {}
 
-class _MockCounter extends Mock implements Counter {}
-
 void main() {
   group('GET /', () {
     test('responds with a 200 and count.', () async {
       const count = 42;
-      final counter = _MockCounter();
-      when(() => counter.value).thenReturn(count.toDouble());
       final context = _MockRequestContext();
-      when(() => context.read<Counter>()).thenReturn(counter);
+      when(() => context.read<int>()).thenReturn(count);
       final response = route.onRequest(context);
       expect(response.statusCode, equals(HttpStatus.ok));
       expect(