Fix useDeferredValue getting stuck (#36134)

Fixes https://github.com/facebook/react/issues/35821

Written/debugged by Claude.

## Test Plan

- Verify undoing the source fix fails the newly added test
- Verify building a bundle with the fix solves
https://github.com/gaearon/react-udv-bug/ repro

DiffTrain build for [c0d218f0f3e02ed581f74096e56baa947213135d](https://github.com/facebook/react/commit/c0d218f0f3e02ed581f74096e56baa947213135d)