feat: add utility functions for date and quantity formatting; refactor inventory and recipe screens to use new formatters

flutter/lib/features/meal_plan/presentation/meal_plan_screen.dart

@@ -6,6 +6,7 @@ import 'package:go_router/go_router.dart';
 import 'package:intl/intl.dart';
 
 import '../../../core/api/api_error_mapper.dart';
+import '../../../core/utils/formatters.dart';
 import '../../../core/l10n/l10n.dart';
 import '../../../core/ui/async_state_views.dart';
 import '../../auth/data/auth_providers.dart';
@@ -591,8 +592,5 @@ class _EnrichedShoppingItem {
     }
   }
 
-  String _formatQuantity(double value) {
-    final normalized = value == value.roundToDouble() ? value.toStringAsFixed(0) : value.toStringAsFixed(1);
-    return normalized.replaceAll(RegExp(r'\.0$'), '');
-  }
+  String _formatQuantity(double value) => formatQuantity(value);
 }