fix: resolve flutter analyze warnings - unused imports, unnecessary casts

test/shared/providers/auth_provider_test.dart

@@ -1,4 +1,3 @@
-import 'dart:async';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:network_app/shared/providers/auth_provider.dart';
@@ -63,7 +62,7 @@ void main() {
     test('initial state checks session', () async {
       when(() => mockApiClient.getSession()).thenAnswer((_) async => null);
 
-      final notifier = container.read(authStateProvider.notifier);
+      final _ = container.read(authStateProvider.notifier);
       
       // Wait for async initialization
       await Future.delayed(Duration.zero);
@@ -101,7 +100,7 @@ void main() {
         'user': {'id': '1', 'email': 'test@test.com'},
       });
 
-      final notifier = container.read(authStateProvider.notifier);
+      final _ = container.read(authStateProvider.notifier);
       
       await Future.delayed(Duration.zero);
       
@@ -126,7 +125,7 @@ void main() {
         'user': {'id': '1', 'email': 'test@test.com', 'name': 'Test User'},
       });
 
-      final notifier = container.read(authStateProvider.notifier);
+      final _ = container.read(authStateProvider.notifier);
       
       await Future.delayed(Duration.zero);
       
@@ -149,7 +148,7 @@ void main() {
       });
       when(() => mockApiClient.signOut()).thenAnswer((_) async {});
 
-      final notifier = container.read(authStateProvider.notifier);
+      final _ = container.read(authStateProvider.notifier);
       
       await Future.delayed(const Duration(milliseconds: 100));
       
@@ -169,7 +168,7 @@ void main() {
         password: any(named: 'password'),
       )).thenThrow(Exception('Invalid credentials'));
 
-      final notifier = container.read(authStateProvider.notifier);
+      final _ = container.read(authStateProvider.notifier);
       
       await Future.delayed(Duration.zero);