The mock_dispatcher fixture's fake_subscribe recorded event handlers
but never called them, causing asyncio.wait() to block for the full
DEFAULT_TIMEOUT (15s) on every test that passes expected_events to
send(). With 28 affected tests, the suite wasted ~8 minutes on dead
waits and required an undocumented pytest-timeout plugin to complete.
Add call_soon to the default fake_subscribe so futures resolve on the
next event loop iteration, matching the pattern already used by
setup_event_response(). Override with a non-resolving mock in
test_send_timeout to preserve timeout path coverage.
Suite now completes in <1 second with no --timeout flag.
