fix: add missing constants import in check_user_service

- Import constants from authorizenet SDK to fix NameError
- Required for setting Authorize.net environment configuration

app/services/check_user_service.py

@@ -1,6 +1,6 @@
 import logging
 import authorizenet.apicontrollers as controllers
-from authorizenet import apicontractsv1
+from authorizenet import apicontractsv1, constants
 
 logger = logging.getLogger(__name__)
 from .. import crud, database, schemas