Created input types.

src/transducer/input.rs

@@ -1,6 +1,10 @@
 use crate::cell::CellView;
 use crate::transducer::Stateful;
 
+pub trait Poll<T: Copy> {
+    async fn poll() -> T;
+}
+
 pub struct StatefulInput<'a, T: Copy> {
     pub state_cell: CellView<'a, T>,
 }