Function start_handshake_server 

pub fn start_handshake_server<F>(port: u16, response_generator: F)
where
    F: Fn() -> String + Send + Sync + 'static + Clone,

Starts a background handshake server on the given port.

The server listens for any incoming TCP connection. For each connection, it attempts to read some data (the “handshake request”). It then responds with a string generated by the response_generator closure.

This function spawns a new thread and returns immediately.