codec: change Encoder to take &Item (#1746)

Co-authored-by: Markus Westerlind <[email protected]>

tokio-util/src/codec/framed_write.rs

@@ -42,7 +42,6 @@ const BACKPRESSURE_BOUNDARY: usize = INITIAL_CAPACITY;
 impl<T, E> FramedWrite<T, E>
 where
     T: AsyncWrite,
-    E: Encoder,
 {
     /// Creates a new `FramedWrite` with the given `encoder`.
     pub fn new(inner: T, encoder: E) -> FramedWrite<T, E> {
@@ -100,7 +99,7 @@ impl<T, E> FramedWrite<T, E> {
 impl<T, I, E> Sink<I> for FramedWrite<T, E>
 where
     T: AsyncWrite,
-    E: Encoder<Item = I>,
+    E: Encoder<I>,
     E::Error: From<io::Error>,
 {
     type Error = E::Error;
@@ -191,9 +190,9 @@ impl<T> FramedWrite2<T> {
 impl<I, T> Sink<I> for FramedWrite2<T>
 where
     T: ProjectFuse + AsyncWrite,
-    T::Codec: Encoder<Item = I>,
+    T::Codec: Encoder<I>,
 {
-    type Error = <T::Codec as Encoder>::Error;
+    type Error = <T::Codec as Encoder<I>>::Error;
 
     fn poll_ready(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
         // If the buffer is already over 8KiB, then attempt to flush it. If after flushing it's