Feature parity review: rclpy-inspired improvements for rclnodejs

[minggangw]

#	Feature	Status	Notes
1	Executor Framework	Skipped	Not needed in rclnodejs. Each Node already has its own background thread via ShadowNode/Executor. Multiple node.spin() calls work independently. Node.js is single-threaded so all JS callbacks are inherently serialized — callback groups are meaningless.
2	Callback Groups	Skipped	Depends on Executor Framework. Node.js single-threaded model means all callbacks are already mutually exclusive by design.
3	waitForMessage() Utility	Implemented	PR #1444. Creates a temporary subscription, resolves on first message, auto-cleans up. Uses TimeoutError for timeout rejection. Extracted to lib/wait_for_message.js.
4	Parameter Event Handler	Implemented	PR #1438. ParameterEventHandler class with per-parameter and event-level callbacks. Refactored ParameterWatcher to use it internally. All Copilot review comments addressed.
5	QoS Overriding via Parameters	Skipped	Narrow use case in Node.js. ROS parameter override mechanism (--ros-args -p ...) is rarely used in JS apps. Users configure QoS in code via config files/env vars. Low effort-to-value ratio.
6	Better spin() API / spinUntilFutureComplete	Dropped	Implemented in PR #1442, then evaluated as syntactic sugar with minimal value. In rclnodejs spin() is non-blocking (unlike rclpy where it blocks), so spin/await/stop is already trivial. Decided to drop in favor of documenting the idiomatic pattern.
7	Signal Handler Guard Condition	Skipped	Not needed. Node.js delivers SIGINT via the libuv event loop to the main thread immediately. The existing process.on('SIGINT') + shutdownAll() mechanism already provides clean, immediate shutdown. The background rcl_wait() thread is woken via StopWaitingHandles(). A guard condition would add complexity without observable benefit.
8	Message Metadata (MessageInfo)	Implemented	PR #1440. Native rclTakeWithInfo binding, MessageInfo class, auto-detection via callback.length >= 2. TypeScript types updated. Copilot review comments addressed.