tls: add opt-in pure-Rust rustls backend behind the TlsBackend trait (tls_backend = rustls; default stays openssl) — TLS1.3, CertFP via handshake-sig verify, SNI, REHASH reload; bump integration timeouts for loaded-host robustness

src/lib.rs

@@ -34,6 +34,7 @@ pub mod resolver;
 pub mod server;
 pub mod socketengine;
 pub mod tls;
+pub mod tls_rustls;
 pub mod users;
 pub mod watch;
 pub mod websocket;