Experiment: Wrap all capnp code in a context-manager to avoid segfaults (#317)

* Experiment: Wrap all capnp code in a context-manager

* Fix segfault in on_disconnect

test/test_rpc_calculator.py

@@ -2,6 +2,7 @@ import gc
 import os
 import socket
 import sys  # add examples dir to sys.path
+import pytest
 
 import capnp
 
@@ -12,6 +13,12 @@ import async_calculator_client  # noqa: E402
 import async_calculator_server  # noqa: E402
 
 
+@pytest.fixture(autouse=True)
+async def kj_loop():
+    async with capnp.kj_loop():
+        yield
+
+
 async def test_calculator():
     read, write = socket.socketpair()
     read = await capnp.AsyncIoStream.create_connection(sock=read)