Small refactor and isort+black formatting

src/pyrmv/errors/int_errors.py

@@ -2,28 +2,33 @@ class IntError(Exception):
     """
     Internal RMV server error.
     """
+
     def __init__(self):
         super().__init__(self.__doc__)
 
     def __str__(self):
         return self.__doc__
 
+
 class IntGatewayError(Exception):
     """
     Communication error with RMV backend systems.
     """
+
     def __init__(self):
         super().__init__(self.__doc__)
 
     def __str__(self):
         return self.__doc__
 
+
 class IntTimeoutError(Exception):
     """
     Timeout during service processing.
     """
+
     def __init__(self):
         super().__init__(self.__doc__)
 
     def __str__(self):
-        return self.__doc__
+        return self.__doc__