tests: add test_recv_results_prepared_v5_reads_metadata_id

Both existing recv_results_prepared tests used protocol_version=4, leaving
the ProtocolVersion.uses_prepared_metadata() branch (v5+) untested.

The new test confirms that on protocol v5, result_metadata_id is read from
the PREPARE response even when use_metadata_id=False (native v5 path).

Author: nikagra

tests/unit/test_protocol.py

@@ -191,7 +191,33 @@ def test_recv_results_prepared_no_extension_skips_metadata_id(self):
         assert msg.query_id == b'ab'
         assert msg.result_metadata_id is None
 
-    def test_recv_results_metadata_changed_flag(self):
+    def test_recv_results_prepared_v5_reads_metadata_id(self):
+        """
+        On protocol v5, ProtocolVersion.uses_prepared_metadata() is True, so
+        result_metadata_id must be read from the PREPARE response even when
+        use_metadata_id is False (native v5 path, not the Scylla extension).
+        """
+        buf = io.BytesIO(
+            struct.pack('>H', 2) + b'ab'   # query_id
+            + struct.pack('>H', 3) + b'xyz'  # result_metadata_id (always present on v5)
+            + struct.pack('>i', 1)           # prepared flags: global_tables_spec
+            + struct.pack('>i', 0)           # colcount = 0
+            + struct.pack('>i', 0)           # num_pk_indexes = 0
+            + struct.pack('>H', 2) + b'ks'  # ksname
+            + struct.pack('>H', 2) + b'tb'  # cfname
+            + struct.pack('>i', 4)           # result flags: no_metadata
+            + struct.pack('>i', 0)           # result colcount = 0
+        )
+
+        features_no_extension = ProtocolFeatures(use_metadata_id=False)
+        msg = ResultMessage(kind=4)  # RESULT_KIND_PREPARED = 4
+        msg.recv_results_prepared(buf, protocol_version=5,
+                                  protocol_features=features_no_extension,
+                                  user_type_map={})
+        assert msg.query_id == b'ab'
+        assert msg.result_metadata_id == b'xyz'
+
+
         """
         When _METADATA_ID_FLAG (0x0008) is set in a ROWS result,
         recv_results_metadata must read and store the new result_metadata_id