PoV Distribution optimization (#1990)

* Initial commit

* Remove unnecessary struct

* Some review nits

* Update node/network/pov-distribution/src/lib.rs

* Update parachain/test-parachains/adder/collator/tests/integration.rs

* Review nits

* notify_all_we_are_awaiting

* Both ways of peers connections should work the same

* Add mod-level docs to error.rs

* Avoid multiple connection requests at same parent

* Dont bail on errors

* FusedStream for ConnectionRequests

* Fix build after merge

* Improve error handling

* Remove whitespace formatting

polkadot/node/subsystem-util/src/validator_discovery.rs

@@ -115,6 +115,12 @@ pub struct ConnectionRequests {
 	requests: StreamUnordered<ConnectionRequest>,
 }
 
+impl stream::FusedStream for ConnectionRequests {
+	fn is_terminated(&self) -> bool {
+		false
+	}
+}
+
 impl ConnectionRequests {
 	/// Insert a new connection request.
 	///
@@ -133,6 +139,11 @@ impl ConnectionRequests {
 			Pin::new(&mut self.requests).remove(token);
 		}
 	}
+
+	/// Is a connection at this relay parent already present in the request
+	pub fn contains_request(&self, relay_parent: &Hash) -> bool {
+		self.id_map.contains_key(relay_parent)
+	}
 }
 
 impl stream::Stream for ConnectionRequests {