Initialize cli/dll_runner variables in Cadet class

Else, there could be errors when deleting the object.

cadet/cadet.py

@@ -213,6 +213,9 @@ def __init__(self, install_path: Optional[Path] = None, use_dll: bool = False, *
         self.cadet_create_lwe_path: Optional[Path] = None
         self.return_information: Optional[dict] = None
 
+        self._cadet_cli_runner: Optional[CadetCLIRunner] = None
+        self._cadet_dll_runner: Optional[CadetDLLRunner] = None
+
         # Regardless of settings in the Meta Class, if we get an install_path, we respect the install_path
         if install_path is not None:
             self.use_dll = use_dll