Use async-exit-stack over contextlib

For `AsyncExitStack`

libp2p/tools/factories.py

@@ -1,7 +1,6 @@
-from contextlib import AsyncExitStack
 from typing import Any, AsyncIterator, Dict, List, Sequence, Tuple, cast
 
-# NOTE: import ``asynccontextmanager`` from ``contextlib`` when support for python 3.6 is dropped.
+from async_exit_stack import AsyncExitStack
 from async_generator import asynccontextmanager
 from async_service import background_trio_service
 import factory

libp2p/tools/pubsub/dummy_account_node.py

@@ -1,6 +1,7 @@
-from contextlib import AsyncExitStack, asynccontextmanager
 from typing import AsyncIterator, Dict, Tuple
 
+from async_exit_stack import AsyncExitStack
+from async_generator import asynccontextmanager
 from async_service import Service, background_trio_service
 
 from libp2p.host.host_interface import IHost

setup.py

@@ -76,6 +76,7 @@ install_requires = [
     "async_generator==1.10",
     "trio>=0.13.0",
     "async-service>=0.1.0a2,<0.2.0",
+    "async-exit-stack==1.0.1",
 ]