fix(iroh-relay): fix client actors not closing

[PaulOlteanu]

Description

When a client actor closes, it awaits Clients::unregister, which then awaits for the actor task to close, so almost every actor task was being leaked. Since the only place Clients::unregister is called is from when the actor is already closing, I chose to break the cycle by not have it call Client::shutdown.

I also added a timeout to the tls handshake because that also gets stuck forever if the client goes away. I didn't add it to the LetsEncrypt acceptor because I wasn't sure where exactly it belonged, but that should probably have one too. I can move this to a separate PR if preferred. Maybe the timeout should be configurable as well?

Notes & open questions

Change checklist

• Self-review.
• Documentation updates following the style guide, if relevant.
• Tests if relevant.
• All breaking changes documented.