Fix code review issues: avoid mutation and fix indentation

Co-authored-by: richardthe3rd <573334+richardthe3rd@users.noreply.github.com>

Author: Copilot

lib/services/festival_service.dart

@@ -21,7 +21,7 @@ class FestivalsResponse {
   factory FestivalsResponse.fromJson(Map<String, dynamic> json, String baseUrl) {
     final festivalsList = (json['festivals'] as List<dynamic>)
         .map((f) {
-          final festivalJson = f as Map<String, dynamic>;
+          final festivalJson = Map<String, dynamic>.from(f as Map<String, dynamic>);
           // Resolve relative URLs to absolute URLs
           if (festivalJson['data_base_url'] != null) {
             final dataBaseUrl = festivalJson['data_base_url'] as String;

test/brewery_screen_test.dart

@@ -60,7 +60,7 @@ void main() {
       final festivalsResponse = FestivalsResponse(
         festivals: [testFestival],
         defaultFestivalId: 'cbf2025',
-            baseUrl: 'https://example.com',
+        baseUrl: 'https://example.com',
         version: '1.0.0',
       );
       when(mockFestivalService.fetchFestivals())