iOS: Scroll freezes entire Rust event loop

Rust events are blocked during iOS scroll. JavaScript continues fine.

This is a minimal reproduction for filing a Tao issue.

Affected (anything using EventLoopProxy to reach the main thread):

• Signal/state updates
• Async task completions
• Cross-thread UI communication

Screen Recording

See included ScreenRecording.mp4

(Red dot = Rust, Green dot = JavaScript)

Run It

dx serve --platform ios

See the Bug

1. Watch red dot spin and counter increment
2. Scroll the page
3. Red dot & counter FREEZE
4. Stop scrolling → catches up instantly

The green dot (JavaScript) keeps spinning while the red dot (Rust) freezes.