test(integration): simplify policy manager retrieval and enhance widget test assertions

Author: dgarciasquare1

test/core/integration_test.dart

@@ -1,9 +1,7 @@
 import 'package:flutter_policy_engine/flutter_policy_engine.dart';
 import 'package:flutter_test/flutter_test.dart';
-import 'package:flutter_policy_engine/src/core/policy_manager.dart';
 import 'package:flutter_policy_engine/src/core/memory_policy_storage.dart';
 import 'package:flutter_policy_engine/src/core/role_evaluator.dart';
-import 'package:flutter_policy_engine/src/exceptions/policy_sdk_exception.dart';
 
 void main() {
   group('Core Integration Tests', () {

test/core/policy_provider_test.dart

@@ -55,8 +55,8 @@ class TestConsumerWidget extends StatelessWidget {
           Builder(
             builder: (context) {
               try {
-                final policyManager = PolicyProvider.policyManagerOf(context);
-                return Text('manager_found: ${policyManager != null}');
+                final _ = PolicyProvider.policyManagerOf(context);
+                return const Text('manager_found: true');
               } catch (e) {
                 return Text('error: ${e.toString()}');
               }
@@ -388,7 +388,7 @@ void main() {
             PolicyProvider(
               policyManager: policyManager,
               child: const Column(
-                children: const [
+                children: [
                   TestConsumerWidget(),
                   TestConsumerWidget(),
                   RebuildTestWidget(),

test/exceptions/policy_sdk_exception_test.dart

@@ -94,7 +94,7 @@ void main() {
       const message = 'Failed to load policy configuration';
 
       // Test with FormatException
-      final formatError = FormatException('Invalid format');
+      const formatError = FormatException('Invalid format');
       final exceptionWithFormatError = PolicySDKException(
         message,
         exception: formatError,