Leverage dirtry rect from cef's accelarated paint api

https://docs.rs/cef-dll-sys/latest/aarch64-apple-darwin/cef_dll_sys/type.cef_accelerated_paint_info_common_t.html#structfield.capture_update_rect

This should save the gpu mem bandwith.

Start by reading the linked CEF accelerated paint API documentation, especially the capture_update_rect field, then locate Graphite's accelerated paint integration. Confirm how update rectangles are currently handled and measure whether using the captured rectangle reduces GPU memory bandwidth. Done means the integration uses the dirty rectangle correctly without breaking rendering.

Written by the indexing model from the issue text.