Implement timer APIs: setTimeout, setInterval, requestAnimationFrame #283

Implements issue 3mhyfo3nvw22s — Timer APIs: setTimeout, setInterval, requestAnimationFrame

Changes #

New module: crates/js/src/timers.rs #

• Thread-local timer registry with sorted pending timers
• Monotonically increasing timer IDs
• Timer lifecycle: schedule, cancel, take due timers, cleanup
• GC root collection for pending timer callbacks

Global functions registered in builtins #

• setTimeout(callback, delay) / clearTimeout(id)
• setInterval(callback, delay) / clearInterval(id)
• requestAnimationFrame(callback) / cancelAnimationFrame(id)

VM event loop integration #

• drain_due_timers() executes due callbacks with microtask drain after each
• pump_event_loop() for single-pass timer drain
• run_event_loop(max_iterations) for running until all timers fire (tests)

Tests (15 tests) #

• Timer ID generation and uniqueness
• Deferred execution (setTimeout(fn, 0) is not synchronous)
• clearTimeout/clearInterval cancellation
• setInterval fires repeatedly and can be stopped
• requestAnimationFrame passes timestamp argument
• Timer callbacks survive GC
• Promise microtasks drain between timer callbacks
• Edge cases (non-function args, invalid IDs)