Vendor dependencies

Let's see how I like this workflow.

vendor/tokio-stream/tests/support/mpsc.rs

@@ -0,0 +1,15 @@
+use async_stream::stream;
+use tokio::sync::mpsc::{self, UnboundedSender};
+use tokio_stream::Stream;
+
+pub fn unbounded_channel_stream<T: Unpin>() -> (UnboundedSender<T>, impl Stream<Item = T>) {
+    let (tx, mut rx) = mpsc::unbounded_channel();
+
+    let stream = stream! {
+        while let Some(item) = rx.recv().await {
+            yield item;
+        }
+    };
+
+    (tx, stream)
+}