feat(process): add Node.js-style event emitter with signal handling

Implement process.on/once/off/emit and related methods for event handling.
Signal events (SIGINT, SIGTERM, etc.) automatically register C signal handlers.

• on, once, addListener, removeListener, off
• removeAllListeners, emit, listenerCount
• setMaxListeners, getMaxListeners (warns at 10 like Node.js)
• Dynamic listener arrays with automatic growth
• O(1) signal name/number lookup via dual hash tables
• GC root tracking for listener functions