Remove unused groupby import

- Removed groupby from itertools imports as it's no longer used
- Keep imports clean and minimal

Co-authored-by: dkropachev <[email protected]>

Author: Copilot

cassandra/policies.py

@@ -15,7 +15,7 @@
 
 from collections import namedtuple, defaultdict
 from functools import lru_cache
-from itertools import islice, cycle, groupby, repeat
+from itertools import islice, cycle, repeat
 import logging
 from random import randint, shuffle
 from threading import Lock