ci: Add and configure isort, and make it happy

ssb/packet_stream.py

@@ -1,15 +1,14 @@
 """Packet streams"""
 
-import logging
-import struct
 from asyncio import Event, Queue
 from enum import Enum
-from time import time
+import logging
 from math import ceil
+import struct
+from time import time
 
 import simplejson
 
-
 logger = logging.getLogger("packet_stream")