Out of memory (editor crash) when loading large images with Vello

When Trying to open a large image in the editor, it crashes after some while. This is likely caused by our animation loop not playing nice with such a long-running task on the main thread

Start by reproducing the crash while opening a large image, then trace the animation loop and image-loading work described in the issue, with attention to tasks running on the main thread. Done means large images no longer cause an out-of-memory editor crash.

索引モデルが issue の本文から書いたものです。