Connection fails when an IPv6 attempt is made before IPv4

[semicoleon]

My simple test case for using this library failed when connecting to a local rabbitmq instance on localhost. I eventually realized that this was due to the AMQPConnectionMultiplexHandler being created outside of the channelInitializer closure (so the IPv6 attempt would fail, and then during the IPv4 attempt the same handler was used which already thought it was closed)

I'm not entirely sure why rabbitmq isn't allowing IPv6 connections on localhost when started with the default config but it seems to be happening consistently for me with RabbitMQ 4.2.2 installed via homebrew on macOS Tahoe.

[semicoleon]

Using the docker-compose.yml in the repo I don't encounter the problem, but if I set RABBITMQ_VERSION=4.2.2 before running docker compose up I do encounter the problem again. Not listening on IPv6 by default might be a change between rabbitmq 3.9.14 and 4.2.2. Fixing the issue in the library seems sensible either way though