Currently the raster cache clears all entries that have not been used at the end of the frame. In the case of SVGs, this can lead to repeated rendering jank in scenarios like a scrolling list or tabbar view where the same picture (pending flutter_svg fix) is continually re-rasterized as a user interacts with the application.

For especially complex pictures (#87826), we should support some method of keeping the cache entry alive past one frame. Some ideas:

• We could tune a threshold for lack of access. Probably flaky, risk optimizing for benchmarks.
• We could tie the entry to the lifetime of the engine Picture object. If the picture isn't disposed, then the framework must be keeping it alive intentionally
• We could provide a new API that returned some sort of raster handle that the framework could manage