Function run_tcp_server 

pub async fn run_tcp_server(
    state: Arc<ServerState>,
    listener: TcpListener,
    conn_timeout: Duration,
) -> Result<(), Box<dyn Error>>

Accept TCP connections and spawn a handler for each.

Callers must bind the TcpListener before spawning any other tasks so that an EADDRINUSE failure is detected eagerly and the beacon is never started.