MQTT5 packet encoder/decoder without std or alloc

Connect packet test query

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