Add test infrastructure with fixtures, helpers, and integration tests

- Add [lib] target to enable integration test imports
- Add rcgen and reqwest dev-dependencies for TLS and HTTP test helpers
- Create src/config/test_fixtures.rs with test_static_config() and test_dynamic_config()
- Create tests/ with integration tests, HTTP test helper (TestUpstream), and TLS test helper (SelfSignedCert)
- Add Clone derives to StaticConfig and related structs for test fixture construction
- All existing tests continue to pass

tests/integration_test.rs

@@ -0,0 +1,32 @@
+mod helpers;
+
+#[tokio::test]
+async fn test_upstream_spawn_and_connect() {
+    let upstream = helpers::http_test_helper::TestUpstream::spawn_ok().await;
+    let client = reqwest::Client::new();
+    let resp = client
+        .get(format!("http://127.0.0.1:{}/", upstream.addr.port()))
+        .send()
+        .await
+        .unwrap();
+    assert_eq!(resp.status(), reqwest::StatusCode::OK);
+    let _ = upstream.shutdown_tx.send(());
+}
+
+#[test]
+fn test_self_signed_cert_generation() {
+    let cert = helpers::tls_test_helper::generate_self_signed_cert(&["test.local"]);
+    assert!(!cert.cert_pem.is_empty());
+    assert!(!cert.key_pem.is_empty());
+    assert!(cert.cert_pem.contains("BEGIN CERTIFICATE"));
+    assert!(cert.key_pem.contains("BEGIN"));
+}
+
+#[test]
+fn test_config_fixtures() {
+    let static_config = reverse_proxy::config::test_fixtures::test_static_config();
+    assert!(!static_config.listeners.is_empty());
+
+    let dynamic_config = reverse_proxy::config::test_fixtures::test_dynamic_config();
+    assert!(!dynamic_config.sites.is_empty());
+}