Fix test failures on Python 3.14 (#394)

* Fix test failures on Python 3.14

As documented at
https://docs.python.org/3/library/asyncio-eventloop.html#asyncio.get_event_loop,
`get_event_loop` now fails if there is no active event loop. Since there
will never already be one at the top level of a file anyway, explicitly
create a new one every time.

* Reformat with black 2026 style

examples/async_server.py

@@ -7,7 +7,6 @@ import logging
 import capnp
 import thread_capnp
 
-
 logger = logging.getLogger(__name__)
 logger.setLevel(logging.DEBUG)