python/iqm: fix subscribing to neighbours, take 2

[ymorin-orange]

Bug fix:

• closes #194

---

How to test:

1. start two MQTT brokers; the socket is considered "local", and 1235 is considered the "neighbour"; start an MQTT client on the local broker:

   $ cat >mosquitto.cfg <<_EOF_
   per_listener_settings true
   listener 0 /tmp/mqtt.sock
   allow_anonymous true
   _EOF_
   $ mosquitto -c mosquitto.cfg
   $ mosquitto -p 1234
   $ mosquitto_sub --unix /tmp/mqtt.sock -t '#' -F '%U %t %p'

2. Install IoT3 Core SDK and its-iqm:
   1. start a docker container with python 3.11 (if you already have python 3.11 or later on your machine, you don't need the container):

      $ docker container run \
          --rm \
          -ti \
          --network host \
          -e http_proxy \
          -e https_proxy \
          -e no_proxy \
          --user $(id -u):$(id -u) \
          --mount type=bind,source=/tmp/mqtt.sock,destination=/tmp/mqtt.sock \
          --mount type=bind,source=$(pwd),destination=$(pwd) \
          --workdir $(pwd) \
          --entrypoint /bin/bash \
          python:3.11.9-slim-bookworm

   2. create and activate a venv to install into:

      (docker)$ python3 -m venv /tmp/iot3
      (docker)$ . /tmp/iot3/bin/activate

   3. install IoT3 Core SDK and its-iqm:

      (docker)$ pip3 --disable-pip-version-check \
          install \
          python/iot3/ \
          python/its-interqueuemanager/

3. Start its-iqm with those configuration files:
   1. its.cfg:

      (docker)$ cat >its.cfg <<_EOF_
      [general]
      instance-id = test-iqm
      prefix = default
      suffix = v2x
      [local]
      socket-path = /tmp/mqtt.sock
      interqueue = interQueue
      [authority]
      type = file
      reload = 5
      path = neighbours.cfg
      _EOF_

   2. neighbours.cfg:

      (docker)$ cat >neighbours.cfg <<_EOF_
      [nghb]
      type = mqtt
      host = localhost
      port = 1234
      prefix = custom
      queue = interQueue
      suffix = v2x
      _EOF_

   3. start its-qm:

      (docker)$ its-iqm -c its.cfg

4. Send a message to interQueue on the neighbour broker:

   $ mosquitto_pub -p 1234 -t custom/interQueue/v2x/cam/1/2/3/0 -m '"test-neighbour"'

---

Expected results:

4. The message on the neighbour broker on interQueue is copied to outQueue on the local broker:

   1729861192.888402253 default/outQueue/v2x/cam/1/2/3/0 "test-neighbour"