Refine Python CI

Add lint environment to `deltachat-rpc-client/`
and set line length to 120, same as in `python/`.

Switch from flake8 to ruff.

Fix ruff warnings.

python/src/deltachat/provider.py

@@ -9,7 +9,8 @@ class ProviderNotFoundError(Exception):
 
 
 class Provider(object):
-    """Provider information.
+    """
+    Provider information.
 
     :param domain: The email to get the provider info for.
     """