test(client): unify fake and real backend testing via BackendPeer

Introduce a BackendPeer abstraction to transparently switch between fake and real IRTT backends. This simplifies test logic by removing manual skip checks and providing a consistent interface for server lifecycle management.

crates/irtt-client/tests/hmac.rs

@@ -9,10 +9,9 @@ use irtt_client::{
 use irtt_proto::{echo_packet_len, ProtoError, TimestampFields};
 
 use support::{
-    config_for_params, default_params, params_for_modes, require_real_backend,
-    run_one_probe_with_config, standard_timestamps, start_bad_hmac_echo_reply_server,
-    start_hmac_close_server, start_hmac_required_open_drop_server, RealIrtServer,
-    ServerObservation, TOKEN,
+    config_for_params, default_params, params_for_modes, run_one_probe_with_config,
+    standard_timestamps, start_bad_hmac_echo_reply_server, start_hmac_close_server,
+    start_hmac_required_open_drop_server, BackendPeer, ServerObservation, TOKEN,
 };
 
 #[test]
@@ -297,14 +296,11 @@ fn assert_no_duplicate_late_or_warning(events: &[ClientEvent]) {
 }
 
 #[test]
-fn real_hmac_correct_key_succeeds() {
-    if !require_real_backend() {
-        return;
-    }
+fn backend_hmac_correct_key_succeeds() {
     let key = b"compat-secret".to_vec();
-    let server = RealIrtServer::start(Some(&key)).unwrap();
     let params = default_params();
-    let mut config = config_for_params(server.addr(), &params);
+    let peer = BackendPeer::start_open_echo(params.clone(), Some(key.clone()));
+    let mut config = config_for_params(peer.addr(), &params);
     config.hmac_key = Some(key);
 
     let mut client = Client::connect(config).unwrap();
@@ -322,13 +318,10 @@ fn real_hmac_correct_key_succeeds() {
 }
 
 #[test]
-fn real_hmac_wrong_key_fails() {
-    if !require_real_backend() {
-        return;
-    }
+fn backend_hmac_wrong_key_fails() {
     let server_key = b"compat-secret".to_vec();
-    let server = RealIrtServer::start(Some(&server_key)).unwrap();
-    let mut config = config_for_params(server.addr(), &default_params());
+    let peer = BackendPeer::start_hmac_required(server_key);
+    let mut config = config_for_params(peer.addr(), &default_params());
     config.open_timeouts = vec![Duration::from_millis(200)];
     config.hmac_key = Some(b"wrong-secret".to_vec());
 
@@ -340,13 +333,10 @@ fn real_hmac_wrong_key_fails() {
 }
 
 #[test]
-fn real_hmac_missing_key_fails() {
-    if !require_real_backend() {
-        return;
-    }
+fn backend_hmac_missing_key_fails() {
     let server_key = b"compat-secret".to_vec();
-    let server = RealIrtServer::start(Some(&server_key)).unwrap();
-    let mut config = config_for_params(server.addr(), &default_params());
+    let peer = BackendPeer::start_hmac_required(server_key);
+    let mut config = config_for_params(peer.addr(), &default_params());
     config.open_timeouts = vec![Duration::from_millis(200)];
     config.hmac_key = None;