Cache error_text() instead of check_error() (#552)

In the case of an error, `check_error()` raises an exception and
there is no return value to cache.

Closes #551

snap7/error.py

@@ -125,7 +125,6 @@ def inner(*args: tuple[Any, ...], **kwargs: dict[Hashable, Any]) -> None:
     return middle
 
 
-@cache
 def check_error(code: int, context: Context = "client") -> None:
     """Check if the error code is set. If so, a Python log message is generated
         and an error is raised.
@@ -143,6 +142,7 @@ def check_error(code: int, context: Context = "client") -> None:
         raise RuntimeError(error)
 
 
+@cache
 def error_text(error: int, context: Context = "client") -> bytes:
     """Returns a textual explanation of a given error number