fix(router): resolve type error on multi-select page navigation

Fixes a `_TypeError` that occurred when navigating to the generic `MultiSelectSearchPage`. The error was caused by an incorrect and overly strict type cast of the `itemBuilder` function within the `GoRouter` configuration.

The solution is to accept the `itemBuilder` as a generic `Function` in the router and then correctly invoke it within the `MultiSelectSearchPage` constructor. This change respects Dart's type system and allows strongly-typed functions (e.g., `(Country) => String`) to be passed without causing a runtime crash.

Author: fulleni

lib/router/router.dart

@@ -33,8 +33,8 @@ import 'package:flutter_news_app_mobile_client_full_source_code/headlines-feed/v
 import 'package:flutter_news_app_mobile_client_full_source_code/headlines-feed/view/headlines_feed_page.dart';
 import 'package:flutter_news_app_mobile_client_full_source_code/headlines-feed/view/headlines_filter_page.dart';
 import 'package:flutter_news_app_mobile_client_full_source_code/headlines-feed/view/manage_saved_filters_page.dart';
-import 'package:flutter_news_app_mobile_client_full_source_code/headlines-feed/view/source_filter_page.dart';
 import 'package:flutter_news_app_mobile_client_full_source_code/headlines-feed/view/source_list_filter_page.dart';
+import 'package:flutter_news_app_mobile_client_full_source_code/headlines-feed/view/source_filter_page.dart';
 import 'package:flutter_news_app_mobile_client_full_source_code/headlines-feed/view/topic_filter_page.dart';
 import 'package:flutter_news_app_mobile_client_full_source_code/headlines-search/bloc/headlines_search_bloc.dart';
 import 'package:flutter_news_app_mobile_client_full_source_code/headlines-search/view/headlines_search_page.dart';
@@ -354,17 +354,19 @@ GoRouter createRouter({
           final initialSelectedItems =
               extra['initialSelectedItems'] as Set<dynamic>? ?? {};
           // The itemBuilder is passed as a function to display the item name.
+          // We accept it as a generic Function and let the page handle the type,
+          // avoiding a strict cast here that causes a _TypeError.
           final itemBuilder =
-              extra['itemBuilder'] as String Function(dynamic item)? ??
-              (item) => item.toString();
+              extra['itemBuilder'] as Function? ??
+              (dynamic item) => item.toString();
 
           // Since this is a generic page, we pass the dynamic types directly.
           // The calling page is responsible for casting the result.
           return MultiSelectSearchPage<dynamic>(
             title: title,
             allItems: allItems,
             initialSelectedItems: initialSelectedItems,
-            itemBuilder: itemBuilder,
+            itemBuilder: (dynamic item) => itemBuilder(item) as String,
           );
         },
       ),