Add idiomatic documentation to Go, Java, Python, and Rust clients

clients/python/src/mxgateway/errors.py

@@ -19,6 +19,7 @@ class MxGatewayError(Exception):
         protocol_status: pb.ProtocolStatus | None = None,
         raw_reply: Any | None = None,
     ) -> None:
+        """Initialize with a message and the optional raw protocol context."""
         super().__init__(message)
         self.protocol_status = protocol_status
         self.raw_reply = raw_reply