Add delim_encode and delim_read

- Add `StreamCommunicator` and `RawConnectionCommunicator`, read/write
messages with delim codec, with `IMuxedStream` and `IRawConnection`
respectively.
- Use it in `Multiselect` and `MultiselectClient`.

libp2p/protocol_muxer/multiselect_communicator_interface.py

@@ -16,7 +16,7 @@ class IMultiselectCommunicator(ABC):
         """
 
     @abstractmethod
-    async def read_stream_until_eof(self) -> str:
+    async def read(self) -> str:
         """
         Reads message from stream until EOF
         """