* CVDisplayLink-plus-GCD * add header * Implement efficient VSync rendering with dirty flag system This commit implements a more efficient VSync rendering approach using a dirty flag system to only render when content actually changes. Key improvements: - Add dirty flag (needs_redraw) to track when rendering is needed - request_redraw() now sets dirty flag instead of immediately queuing - VSync callback only triggers redraw when window is dirty - Direct view pointer access for efficient state checking (no locks) - Maintains perfect VSync timing while reducing unnecessary work Benefits: - Power efficient: No redraws when content is static - Perfect VSync: Hardware-synchronized timing eliminates tearing - Multi-display support: Adapts to different refresh rates automatically - Event queue efficiency: Reduces unnecessary event processing Architecture changes: - CVDisplayLink → GCD → check dirty → conditional queue_redraw() - Added get_window_delegate() function for view-to-delegate access - Enhanced DisplayLinkUserData with view pointer - Added NSWindow.delegate() method binding This brings Rio's rendering efficiency to a new level while maintaining the existing event-driven architecture. * remove VSYNC_IMPLEMENTATION_SUMMARY.md * add note for README * fix lint