patch method
Apply a partial update ("patch") to an existing entity.
Implementation
@override
Future<T> patch({required String id, required Map<String, dynamic> delta, String? userId}) async {
final existing = _storage[userId ?? '']?[id];
if (existing == null) {
throw EntityNotFoundException(message: 'Entity $id not found for user ${userId ?? ''}.');
}
final patched = fromMap(existing.toDatumMap()..addAll(delta));
await update(patched);
return patched;
}