PDF pages rendered blank while scrolling in scrolled mode (#4795,
resurfacing #4031). On-device profiling showed each page takes hundreds
of ms to render while the preload margin gave only about half a page of
lead, and loads were unbounded and unprioritized.
Bump the foliate-js submodule to widen the scrolled-mode preload margin
and drive page loading through a bounded, viewport-prioritized scheduler
(readest/foliate-js#40). Adds unit coverage for the new planScrollModePages
scheduler.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Huang Xin