feat: add UTC parsing utilities and update date handling across entities

- Introduced `utc_parser.dart` with functions to convert UTC timestamps to local time.
- Updated date parsing in various entities to use the new utility functions for consistency.
- Refactored date handling in `BenefitHistory`, `Business`, `AttendanceStatus`, `AssignedWorker`, `TimeRange`, `Invoice`, `PaymentChartPoint`, `StaffPayment`, `TimeCardEntry`, `OrderItem`, `OrderPreview`, `RecentOrder`, `StaffRating`, `CoverageDayPoint`, `ForecastWeek`, `NoShowIncident`, `SpendDataPoint`, `AssignedShift`, `CancelledShift`, `CompletedShift`, `OpenShift`, `PendingAssignment`, `Shift`, `ShiftDetail`, `TodayShift`, `BusinessMembership`, and `Staff`.
- Updated `ReorderWidget` and `OrderEditSheet` to handle date formatting correctly.

apps/mobile/packages/core/lib/src/services/api_service/inspectors/auth_interceptor.dart

@@ -32,7 +32,7 @@ class AuthInterceptor extends Interceptor {
     if (!skipAuth) {
       final User? user = FirebaseAuth.instance.currentUser;
       if (user != null) {
-        final String? token = await user.getIdToken();
+        final String? token =  await user.getIdToken();
         if (token != null) {
           options.headers['Authorization'] = 'Bearer $token';
         }

apps/mobile/packages/core/lib/src/utils/date_time_utils.dart

@@ -4,4 +4,9 @@ class DateTimeUtils {
   static DateTime toDeviceTime(DateTime date) {
     return date.toLocal();
   }
+
+  /// Converts a local [DateTime] back to UTC for API payloads.
+  static String toUtcIso(DateTime local) {
+    return local.toUtc().toIso8601String();
+  }
 }