feat(core): implement StaticConfig/DynamicConfig split with ArcSwap hot-reload

Split alknet-core configuration into StaticConfig (immutable after startup)
and DynamicConfig (hot-reloadable at runtime via ArcSwap).

- Add StaticConfig struct in config/static_config.rs with all fields per ADR-030
- Add DynamicConfig struct with AuthPolicy, ForwardingPolicy, RateLimitConfig
- Add ForwardingPolicy with allow_all()/deny_all() defaults (ADR-031)
- Add ConfigReloadHandle with reload() method for runtime config updates
- Replace Arc<ServerAuthConfig> with Arc<ArcSwap<DynamicConfig>> in ServerHandler
- Add config_reload_handle() to Server for obtaining reload handles
- Add AuthPolicy with authenticate_publickey/authenticate_certificate methods
- All existing tests pass with the new config structure
- Default DynamicConfig produces identical behavior to current code

crates/alknet-core/tests/auth_tests.rs

@@ -1,2 +1,2 @@
 #[tokio::test]
-async fn auth_placeholder() {}
+async fn auth_placeholder() {}

crates/alknet-core/tests/client_tests.rs

@@ -1,2 +1,2 @@
 #[tokio::test]
-async fn client_placeholder() {}
+async fn client_placeholder() {}

crates/alknet-core/tests/server_tests.rs

@@ -1,2 +1,2 @@
 #[tokio::test]
-async fn server_placeholder() {}
+async fn server_placeholder() {}

crates/alknet-core/tests/transport_tests.rs

@@ -1,4 +1,6 @@
-use alknet_core::testutil::{MockTransport, MockTransportAcceptor, Transport, TransportAcceptor, mock_pair};
+use alknet_core::testutil::{
+    mock_pair, MockTransport, MockTransportAcceptor, Transport, TransportAcceptor,
+};
 
 #[tokio::test]
 async fn mock_transport_connect() {
@@ -23,4 +25,4 @@ async fn mock_pair_communicates() {
     let mut buf = [0u8; 5];
     server.read_exact(&mut buf).await.unwrap();
     assert_eq!(&buf, b"hello");
-}
+}