Cookbook: tls-echo
```bash
cargo run -p tls-echo -- 127.0.0.1:8443
# openssl s_client -connect 127.0.0.1:8443 -alpn echoSource: examples/tls-echo. Self-signed PEM via rcgen + acceptor_from_pem, then TcpListenerConfig::with_tls.
```bash
cargo run -p tls-echo -- 127.0.0.1:8443
# openssl s_client -connect 127.0.0.1:8443 -alpn echoSource: examples/tls-echo. Self-signed PEM via rcgen + acceptor_from_pem, then TcpListenerConfig::with_tls.