feat: add unsubscribe ack packet to the unsubscribe callback (#1922)

* Invoke the unsubscribe ack callback with the Unsuback packet, not null

* Don't verify incorrect behavior

---------

Co-authored-by: Daniel Lando <daniel.sorridi@gmail.com>

src/lib/handlers/ack.ts

@@ -144,7 +144,7 @@ const handleAck: PacketHandler = (client, packet) => {
 			delete client.outgoing[messageId]
 			client.messageIdProvider.deallocate(messageId)
 			client['_invokeStoreProcessingQueue']()
-			cb(null)
+			cb(null, packet)
 			break
 		}
 		default:

test/abstract_client.ts

@@ -1974,7 +1974,7 @@ export default function abstractTest(server, config, ports) {
 			client.once('connect', () => {
 				// callback args can be typed
 				client.unsubscribe(topic, (_, packet?: mqtt.Packet) => {
-					assert.isUndefined(packet)
+					assert.isDefined(packet)
 					client.end(true, done)
 				})
 			})