Important RingBuffBytesSender fix on non batched mode! & downgrade nix-shell python to lowest supported

default.nix

@@ -13,6 +13,6 @@ pkgs.mkShell {
 
   shellHook = ''
     set -e
-    uv venv .venv --python=3.12
+    uv venv .venv --python=3.11
   '';
 }

tractor/ipc/_ringbuf.py

@@ -512,6 +512,7 @@ class RingBuffBytesSender(trio.abc.SendChannel[bytes]):
         msg: bytes = struct.pack("<I", len(value)) + value
         if self.batch_size == 1:
             await self._sender.send_all(msg)
+            return
 
         self._batch += msg
         self._batch_msg_len += 1