fix: restore notifier variable + fix unnecessary_null_comparison

test/shared/providers/auth_provider_test.dart

@@ -62,7 +62,8 @@ void main() {
     test('initial state checks session', () async {
       when(() => mockApiClient.getSession()).thenAnswer((_) async => null);
 
-      final _ = container.read(authStateProvider.notifier);
+      // ignore: unused_local_variable
+      final notifier = container.read(authStateProvider.notifier);
       
       // Wait for async initialization
       await Future.delayed(Duration.zero);
@@ -100,7 +101,7 @@ void main() {
         'user': {'id': '1', 'email': 'test@test.com'},
       });
 
-      final _ = container.read(authStateProvider.notifier);
+      final notifier = container.read(authStateProvider.notifier);
       
       await Future.delayed(Duration.zero);
       
@@ -125,7 +126,7 @@ void main() {
         'user': {'id': '1', 'email': 'test@test.com', 'name': 'Test User'},
       });
 
-      final _ = container.read(authStateProvider.notifier);
+      final notifier = container.read(authStateProvider.notifier);
       
       await Future.delayed(Duration.zero);
       
@@ -148,7 +149,7 @@ void main() {
       });
       when(() => mockApiClient.signOut()).thenAnswer((_) async {});
 
-      final _ = container.read(authStateProvider.notifier);
+      final notifier = container.read(authStateProvider.notifier);
       
       await Future.delayed(const Duration(milliseconds: 100));
       
@@ -168,7 +169,7 @@ void main() {
         password: any(named: 'password'),
       )).thenThrow(Exception('Invalid credentials'));
 
-      final _ = container.read(authStateProvider.notifier);
+      final notifier = container.read(authStateProvider.notifier);
       
       await Future.delayed(Duration.zero);