Migrate to aiomqtt

[bj00rn]

Replace gmqtt with aiomqtt (async wrapper around paho-mqtt). I have major issues with getting TLS working when running broker behind reverse proxy. I've scoured the Issues section at gmqtt and TLS support seems patchy.

Sorry for spamming PRs 🤓

Rationale

Might seem a bit backward since the resent migration from paho-mqtt but aiomqtt is a wrapper around paho with async support.

gmqtt

seems to have patchy TLS support
not well maintained

aiomqtt (aka mqtt-asyncio)

well maintained 3+ releases 2025
good community support since uses underlying paho-mqtt
Working TLS
supports websockets and unix file connections

Changes in this PR

• Use aiomqtt
• Stop sending keepalive and instead set retain=True, qos=1 for birth message.
• Set qos=1 for LWT
• Fix deault port mapping for TLS

[nanomad]

@bj00rn I'm just back from vacation. I'll postpone this for the next release

[bj00rn]

@nanomad had a look yet? I just did a rebase to fix lock file

[bj00rn]

@nanomad Feeling quite confident that this is ready for merge if you are interested. I've been running this locally for a while now. aiomqtt feels solid.

Had some issues with the Birth/keepalive and LWT. The client now sends birth message with retain=True qos=1 on connect. (Not sure if qos is strictly necessary). I've updated the send_* functions to support these options.

If this PR is accepted i could rework the subscription logic as subscription, no need to resubscribe on reconnect since aiomqtt client is reusable by default.