feat: add wait

crates/mad/src/lib.rs

@@ -85,6 +85,12 @@ impl Mad {
         self
     }
 
+    pub fn add_wait(&mut self) -> &mut Self {
+        self.components.push(Waiter::default().into_component());
+
+        self
+    }
+
     pub fn add_fn<F, Fut>(&mut self, f: F) -> &mut Self
     where
         F: Fn(CancellationToken) -> Fut + Send + Sync + 'static,

crates/mad/src/waiter.rs

@@ -5,10 +5,26 @@ use tokio_util::sync::CancellationToken;
 
 use crate::{Component, MadError};
 
+pub struct DefaultWaiter {}
+#[async_trait]
+impl Component for DefaultWaiter {
+    async fn run(&self, _cancellation_token: CancellationToken) -> Result<(), MadError> {
+        panic!("should never be called");
+    }
+}
+
 pub struct Waiter {
     comp: Arc<dyn Component + Send + Sync + 'static>,
 }
 
+impl Default for Waiter {
+    fn default() -> Self {
+        Self {
+            comp: Arc::new(DefaultWaiter {}),
+        }
+    }
+}
+
 impl Waiter {
     pub fn new(c: Arc<dyn Component + Send + Sync + 'static>) -> Self {
         Self { comp: c }