util: document cancel safety of SinkExt::send and StreamExt::next (#6417)

tokio-util/src/codec/framed_read.rs

@@ -17,9 +17,15 @@ pin_project! {
     /// For examples of how to use `FramedRead` with a codec, see the
     /// examples on the [`codec`] module.
     ///
+    /// # Cancellation safety
+    /// * [`tokio_stream::StreamExt::next`]: This method is cancel safe. The returned
+    /// future only holds onto a reference to the underlying stream, so dropping it will
+    /// never lose a value.
+    ///
     /// [`Stream`]: futures_core::Stream
     /// [`AsyncRead`]: tokio::io::AsyncRead
     /// [`codec`]: crate::codec
+    /// [`tokio_stream::StreamExt::next`]: https://docs.rs/tokio-stream/latest/tokio_stream/trait.StreamExt.html#method.next
     pub struct FramedRead<T, D> {
         #[pin]
         inner: FramedImpl<T, D, ReadFrame>,