Implement descriptor multiplexing (select, poll, epoll)

[pbalduino]

Goal

Add I/O multiplexing support to monitor multiple file descriptors efficiently.

Context

No descriptor multiplexing exists. Programs cannot wait for I/O on multiple fds.

Definition of Done

• [ ] select() / pselect() - Wait on multiple fds (POSIX)
• [ ] poll() / ppoll() - Alternative multiplexing API
• [ ] epoll_create() / epoll_ctl() / epoll_wait() - Linux-style efficient multiplexing
• [ ] Kernel poll infrastructure
• [ ] Support in device drivers (poll ops)
• [ ] Edge-triggered and level-triggered modes (epoll)

Dependencies

Required

• #193 - Minimal libc ✅
• #96 - File descriptor management ✅
• Kernel poll infrastructure (needs implementation)

Priority

Medium-High - Critical for servers and event-driven programs

Estimated Time

8-12 weeks part-time (needs kernel infrastructure)