refactor(engine): flatten

- add `just stats`
- add basic doctests

engine/jack_types.rs

@@ -0,0 +1,27 @@
+use crate::*;
+
+/// Running JACK [AsyncClient] with maximum type erasure.
+///
+/// One [Box] contains function that handles [JackEvent]s.
+///
+/// Another [Box] containing a function that handles realtime IO.
+///
+/// That's all it knows about them.
+pub type DynamicAsyncClient<'j>
+    = AsyncClient<DynamicNotifications<'j>, DynamicAudioHandler<'j>>;
+
+/// Notification handler wrapper for [BoxedAudioHandler].
+pub type DynamicAudioHandler<'j> =
+    ClosureProcessHandler<(), BoxedAudioHandler<'j>>;
+
+/// Boxed realtime callback.
+pub type BoxedAudioHandler<'j> =
+    Box<dyn FnMut(&Client, &ProcessScope) -> Control + Send + Sync + 'j>;
+
+/// Notification handler wrapper for [BoxedJackEventHandler].
+pub type DynamicNotifications<'j> =
+    JackNotify<BoxedJackEventHandler<'j>>;
+
+/// Boxed [JackEvent] callback.
+pub type BoxedJackEventHandler<'j> =
+    Box<dyn Fn(JackEvent) + Send + Sync + 'j>;