Proposal: integrate Pretext for DOM-free text height measurement

Looked through MessageList.jsx and noticed getBoundingClientRect()
is being called in two places, scrollToEnd and scroll anchoring, which triggers layout reflow on every new message.
There's a new library called Pretext (@chenglou/pretext) by Cheng Lou
(ex React core team) that calculates text height using pure JS math
instead of DOM measurements. It's sub-millisecond after the initial
prepare() call.
Two potential improvements here:
-cleaner scroll anchoring without waiting for DOM to settle
-groundwork for virtualization if that's ever on the roadmap
(virtualization needs heights before render, which is exactly
what Pretext provides)
Can start with a small proof of concept PR if you're open to it.

Start with MessageList.jsx and inspect the two getBoundingClientRect() call sites in scrollToEnd and scroll anchoring. Review Pretext's prepare() usage, then compare a proof of concept with the existing DOM measurements. Done would be a demonstrated integration that preserves scrolling behavior and establishes whether pre-render text heights are usable.

Written by the indexing model from the issue text.