feat(backend) scheduler rewrite (deadlock for now)

backend/server/src/scheduler/task_func.rs

@@ -1,3 +1,15 @@
+use std::pin::Pin;
+
 pub trait TaskFunc: Fn() + Send + Sync + 'static {}
 
 impl<T> TaskFunc for T where T: Fn() + Send + Sync + Clone + 'static {}
+
+pub trait AsyncTaskFunc:
+    Fn() -> Pin<Box<dyn Future<Output = ()> + Send>> + Send + Sync + 'static
+{
+}
+
+impl<T> AsyncTaskFunc for T where
+    T: Fn() -> Pin<Box<dyn Future<Output = ()> + Send>> + Send + Sync + Clone + 'static
+{
+}