event: add a simple wrapper around sd-event

In order to facilitate stop-conditions on the async::context,
we need to be able to escape the wait on the dbus fd.  sd-event
will allow us to do this and also build other co-routine primitives
in the future (such as `co_await async::delay(1s)` backed by sd-event
timers).  Define a simple wrapper around sd-event here which can
be leveraged by the async framework.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I945416cbce3c98d98135c42cb7ca249a57cb9a60
diff --git a/test/meson.build b/test/meson.build
index 4d3114c..e62c1e7 100644
--- a/test/meson.build
+++ b/test/meson.build
@@ -23,6 +23,7 @@
     'async/task',
     'bus/list_names',
     'bus/match',
+    'event/event',
     'exception/sdbus_error',
     'message/append',
     'message/call',