[AIO] Implement SASL PLAIN with expect() flow

[hifi]

SASL PLAIN is a simple authentication flow that needs to be done before registering a connection. This works on networks like Libera.Chat.

Downstream implementation here using an expect() flow: https://github.com/hifi/heisenbridge/blob/master/heisenbridge/irc.py#L122

Depends on #189 to be fixed first.