Better test packet logging & validation

Summary:
related to T12015, T11798
- improved packet logging in test broker for easier debugging
- test broker will fail the test if a packet is sent after all the messages were exchanged
- fixed a bug in assemble_op where read buffer was not properly cleared if an error occurred (for example, malformed packet cases)

Reviewers: ivica

Reviewed By: ivica

Subscribers: iljazovic, miljen

Differential Revision: https://repo.mireo.local/D27561

test/integration/read_message.cpp

@@ -30,9 +30,8 @@ void test_receive_malformed_packet(
 		reason_codes::malformed_packet.value(), dc_props
 	);
 
-	test::msg_exchange broker_side;
 	error_code success {};
-
+	test::msg_exchange broker_side;
 	broker_side
 		.expect(connect)
 			.complete_with(success, after(0ms))