extract publisher and subscriber

Author: pavel-kirienko

CLAUDE.md

@@ -31,6 +31,8 @@ Key mechanisms in `Node`:
 - **Gossip**: Periodic and urgent data exchange to keep CRDT consistent.
 - **Deduplication, Reordering, Reliable delivery** of user messages.
 
+Use `nox` to run the full test suite.
+
 ## Conventions
 
 - **Formatting**: PEP8, Black, line-length=120.

src/pycyphal/__init__.py

@@ -19,7 +19,9 @@
     name_normalize,
     name_resolve,
 )
-from ._node import Arrival, Breadcrumb, Node, Publisher, Response, ResponseStream, Subscriber, Topic
+from ._node import Node, Topic
+from ._publisher import Publisher, Response, ResponseStream
+from ._subscriber import Arrival, Breadcrumb, Subscriber
 from ._transport import (
     SUBJECT_ID_MODULUS_17bit,
     SUBJECT_ID_MODULUS_23bit,