p2p: fail cleanly when listen bind fails

[mooncitydev]

what was wrong

the http api server already checks TcpListener::bind and prints an error if the port cannot be opened. the p2p listener did .unwrap() on the same operation, so a busy port or other bind error crashed the whole process with a panic.

what changed

• P2PManage::server now returns io::Result instead of panicking.
• event_loop prints a clear message and returns errf! like the api server path, so operators get a normal shutdown path instead of a thread panic.

this matches the behavior of server_listen in the server crate.

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made by mooncitydev