Event worker for Erlang-native asyncio event loop.

This gen_server implements the scalable I/O model with one worker per Python context. Each worker: - Receives {select, FdRes, Ref, ready_input|ready_output} directly from enif_select - Handles {timeout, TimerRef} messages for timer dispatch - Manages timers via erlang:send_after to self()

Owns: the readiness and timer messages of one loop, and its task_ready coalescing. Talks to: the py_event_loop.c NIFs (process_ready_tasks, timers), py_event_worker_registry. Never: runs the loop itself in owngil mode (the context thread does) and never blocks on Python.