Forward on_idle_timeout to WebSocketLifecycleEventReceiver

Lori delivers idle timeout events to WebSocketServer, but all four
connection states discarded them. This adds the final hop from the
_Open state to user code, following the existing on_throttled/
on_unthrottled pattern.

Closes #25

Author: SeanTAllen

.release-notes/forward-on-idle-timeout.md

@@ -0,0 +1,11 @@
+## Forward on_idle_timeout to WebSocketLifecycleEventReceiver
+
+`WebSocketLifecycleEventReceiver` now includes an `on_idle_timeout()` callback, fired when lori's idle timeout triggers on an open connection. This lets connection actors react to idle timeouts — for example, to implement heartbeat-based dead connection detection.
+
+The callback has a default no-op implementation, so existing code is unaffected. Override it in your `WebSocketServerActor` to handle idle timeouts:
+
+```pony
+fun ref on_idle_timeout() =>
+  // Connection went idle — close it
+  _ws.close()
+```

mare/_connection_state.pony

@@ -83,7 +83,9 @@ primitive _Open is _ConnectionState
     server._fire_on_unthrottled()
 
   fun on_sent(server: WebSocketServer ref, token: lori.SendToken) => None
-  fun on_idle_timeout(server: WebSocketServer ref) => None
+
+  fun on_idle_timeout(server: WebSocketServer ref) =>
+    server._fire_on_idle_timeout()
 
   fun send_text(server: WebSocketServer ref, data: String val) =>
     server._send_frame(_FrameEncoder.text(data))

mare/web_socket_lifecycle_event_receiver.pony

@@ -65,3 +65,7 @@ trait WebSocketLifecycleEventReceiver
   fun ref on_unthrottled() =>
     """Called when backpressure is released on the connection."""
     None
+
+  fun ref on_idle_timeout() =>
+    """Called when the connection's idle timeout fires."""
+    None

mare/web_socket_server.pony

@@ -353,3 +353,9 @@ class WebSocketServer is lori.ServerLifecycleEventReceiver
     | let r: WebSocketLifecycleEventReceiver ref => r.on_unthrottled()
     | None => _Unreachable()
     end
+
+  fun ref _fire_on_idle_timeout() =>
+    match \exhaustive\ _lifecycle_event_receiver
+    | let r: WebSocketLifecycleEventReceiver ref => r.on_idle_timeout()
+    | None => _Unreachable()
+    end