use string config instead of writeIO magic

merge ontop of !717 (merged)

saqc/parsing/reader.py

@@ -81,6 +81,7 @@ def fromConfig(fname, *args, **func_kwargs):
 class _ConfigReader:
     logger: logging.Logger
     saqc: SaQC
+    file: str | None
     config: pd.DataFrame | None
     parsed: List[Tuple[Any, ...]] | None
     regex: bool | None