fix(peer): handle UploadDenied so refused downloads fail fast

Peer message code 50 had no handler, so the dispatcher dropped it and a
download refused by the peer stayed Queued until the caller's timeout.

The new handler reads the filename and reason and routes the denial into
the same failure path as UploadFailed. A reason of "Queued" is status,
not a failure: some clients send it for a download that is still held in
their queue, and failing it would kill healthy downloads after a
reconnect, so that one is only logged.

Fixes #29

soulseek-rs-lib/src/actor/peer_actor.rs

@@ -5,7 +5,7 @@ use crate::message::peer::{
     FileSearchResponse, GetShareFileList, PeerInit, PlaceInQueueRequest,
     PlaceInQueueResponse, QueueUploadHandler, SharedDirectory,
     SharedFileListResponseHandler, TransferRequest, TransferResponse,
-    UploadFailedHandler,
+    UploadDeniedHandler, UploadFailedHandler,
 };
 use crate::message::server::MessageFactory;
 use crate::message::{Handlers, Message, MessageReader, MessageType};
@@ -178,6 +178,7 @@ impl PeerActor {
         handlers.register_handler(TransferRequest);
         handlers.register_handler(TransferResponse);
         handlers.register_handler(GetShareFileList);
+        handlers.register_handler(UploadDeniedHandler);
         handlers.register_handler(UploadFailedHandler);
         handlers.register_handler(PlaceInQueueRequest);
         handlers.register_handler(PlaceInQueueResponse);