Support for reverse connections

First of all let me say this seems like a really interesting project!

One thing I think it could also be useful for is remote access to IoT devices. IoT devices often sit behind a NAT and only have outbound HTTP access. Granted, sometimes they might not even have outbound HTTP/3 access due to UDP restrictions but I think those days are numbered and those cases are limited. These devices sometimes also have laggy Internet connections over 2G (for which SSH3 seems like a good fit). Therefore it would be beneficial if SSH3 supported a reverse persistent connection. Where the "client" sets up a persistent connection to a server (like for example autossh).