feat: implement sleep/delay function

[mjm918]

Summary

Add sleep/delay capability to naml runtime for timing control in games and applications.

Proposed API

// Sleep for specified milliseconds
fn sleep(ms: int);

Use Cases

• Game loops (controlling frame rate)
• Rate limiting
• Animations
• Polling intervals

Implementation Notes

• Block execution for specified duration
• Platform considerations:
  • Native: std::thread::sleep
  • Server WASM: WASI poll_oneoff or busy wait
  • Browser: Not directly applicable (use async/setTimeout)

Acceptance Criteria

• sleep(ms) pauses execution for approximately ms milliseconds
• Accepts values from 0 to at least 60000 (1 minute)
• Works on native platform

[mjm918]

Implemented. sleep(ms) is a built-in function.