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

clients/python/src/mxgateway/options.py

@@ -23,6 +23,7 @@ class ClientOptions:
     stream_timeout: float | None = None
 
     def __post_init__(self) -> None:
+        """Validate options; raise `ValueError` for invalid combinations."""
         if not self.endpoint:
             raise ValueError("endpoint must not be empty")
 
@@ -34,6 +35,7 @@ class ClientOptions:
             raise ValueError("stream_timeout must be greater than zero")
 
     def __repr__(self) -> str:
+        """Return a repr that redacts the API key value."""
         api_key = REDACTED if self.api_key else None
         return (
             f"{type(self).__name__}(endpoint={self.endpoint!r}, "