Class RAFTicker

Ticker based on requestAnimationFrame with a configurable interval. Optimized for browser environments. Falls back to setTimeout when RAF is unavailable.

Key features:

• Leading edge: the first callback is invoked in the first frame (via _startTime offset)
• Safe stop() inside callback: _startTime is recalculated BEFORE calling callback
• If callback calls stop() synchronously, the frame is not rescheduled