test: verify all node fields in ServersResponse round-trip test

The test only checked 3 of 9 node fields (node 0's id/address and
node 1's role). A decoder bug affecting inter-node boundary
handling after the first node's address padding would go undetected.
Now verifies all fields for all nodes using a loop.

Closes #171.

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

Author: antoineleclair

tests/test_messages_responses.py

@@ -1046,9 +1046,10 @@ def test_roundtrip(self) -> None:
         encoded = msg.encode()
         decoded = ServersResponse.decode_body(encoded[HEADER_SIZE:])
         assert len(decoded.nodes) == 3
-        assert decoded.nodes[0].node_id == 1
-        assert decoded.nodes[0].address == "node1:9001"
-        assert decoded.nodes[1].role == 2
+        for i, expected in enumerate(nodes):
+            assert decoded.nodes[i].node_id == expected.node_id
+            assert decoded.nodes[i].address == expected.address
+            assert decoded.nodes[i].role == expected.role
 
     def test_wire_format_starts_with_count(self) -> None:
         """Body must start with uint64 node count per Go reference."""