[DevTools] Use Inline Snapshots for storeStressTestSync (#24583)

Change storeStressTestSync to use inline snapshots instead of a snapshot file. We want to do this because some tests are gated and not called in regression tests, and if snapshot tests are not called when there is a corresponding .snap file, that test will fail.

Arguably inline snapshots are a better pattern anyway, so enforcing this in DevTools tests IMO makes sense

Author: lunaruan