refactor: Move SubInfo to stream_subscription.py.

zerver/lib/stream_subscription.py

@@ -16,6 +16,12 @@ from zerver.models import (
 )
 
 
+@dataclass
+class SubInfo:
+    user: UserProfile
+    sub: Subscription
+    stream: Stream
+
 @dataclass
 class SubscriberPeerInfo:
     subscribed_ids: Dict[int, Set[int]]