feat: Add DateTimeUtils for converting UTC to device local time and update imports

apps/mobile/packages/core/lib/core.dart

@@ -2,3 +2,4 @@ library core;
 
 export 'src/domain/arguments/usecase_argument.dart';
 export 'src/domain/usecases/usecase.dart';
+export 'src/utils/date_time_utils.dart';

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

@@ -0,0 +1,7 @@
+
+class DateTimeUtils {
+  /// Converts a [DateTime] (assumed UTC if not specified) to the device's local time.
+  static DateTime toDeviceTime(DateTime date) {
+    return date.toLocal();
+  }
+}