docs: fix MetadataResponse docstring — node metadata, not statement

The docstring incorrectly said "Statement metadata response" but
MetadataResponse carries failure_domain and weight, which are
node-level cluster topology properties returned by DescribeRequest.

Closes #168.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: antoineleclair

src/dqlitewire/messages/responses.py

@@ -547,7 +547,10 @@ def decode_body(cls, data: bytes, schema: int = 0) -> "ServersResponse":
 
 @dataclass
 class MetadataResponse(Message):
-    """Statement metadata response.
+    """Node metadata response (failure domain and weight).
+
+    Returned in response to a DescribeRequest. Contains the node's
+    failure domain and weight, used for cluster topology decisions.
 
     Body: uint64 failure_domain, uint64 weight
     """