MQTT5 packet encoder/decoder without std or alloc

Connect packet test query

bash mosquitto_pub -m "test" -t "test" -i test_id \ -u iz \ -P 1234 \ --will-topic "will" \ --will-payload "lastwill" \ --will-qos 2 \ --will-retain \ -D will response-topic "will_respond" \ -D will content-type "text" \ -D will correlation-data "1234" \ -D will message-expiry-interval 120 \ -D will payload-format-indicator 2 \ -D will user-property "sfilename" "test.txt" \ -D will will-delay-interval 5 -V 5