Clarify comment about restoring paging_state

Rephrase the comment to explain specifically what the restoration
prevents: affecting subsequent uses of the QueryMessage object if
it's reused elsewhere in the codebase.

Co-authored-by: mykaul <4655593+mykaul@users.noreply.github.com>

Author: Copilot

cassandra/cluster.py

@@ -3748,7 +3748,7 @@ def _fetch_all_pages(self, connection, result, query_msg, timeout):
                 result.parsed_rows = all_rows
             return result
         finally:
-            # Restore original paging_state to avoid side effects
+            # Restore original paging_state to prevent affecting subsequent uses of this QueryMessage
             query_msg.paging_state = original_paging_state
 
     def shutdown(self):