feat(rustproxy-http): add HTTP/2 auto-detection via ALPN with TTL-backed protocol cache and h1-only/h2 ALPN client configs

rust/crates/rustproxy/tests/common/mod.rs

@@ -195,7 +195,10 @@ pub async fn start_tls_http_backend(
 ) -> JoinHandle<()> {
     use std::sync::Arc;
 
-    let acceptor = rustproxy_passthrough::build_tls_acceptor(cert_pem, key_pem)
+    // Use h1-only acceptor: test backends speak raw HTTP/1.1 text,
+    // so they must NOT advertise h2 via ALPN (which would cause
+    // auto-detect to attempt h2 binary framing and fail).
+    let acceptor = rustproxy_passthrough::build_tls_acceptor_h1_only(cert_pem, key_pem)
         .expect("Failed to build TLS acceptor");
     let acceptor = Arc::new(acceptor);
     let name = backend_name.to_string();