style: Add blank lines for better readability in sendchat.py

aider/sendchat.py

@@ -15,6 +15,7 @@ CACHE = None
 
 RETRY_TIMEOUT = 60
 
+
 def sanity_check_messages(messages):
     """Check if messages alternate between user and assistant roles.
     System messages can be interspersed anywhere.
@@ -29,6 +30,7 @@ def sanity_check_messages(messages):
         last_role = role
     return True
 
+
 def send_completion(
     model_name,
     messages,