Follow up Android snapshot helper reliability and performance

[thymikee]

Context

PR #454 adds the Android snapshot helper and keeps it helper-first with stock UIAutomator fallback. During review we intentionally kept a few non-blocking improvements out of the PR to avoid overengineering the first release.

Follow-ups

• Add a per-device/per-helper-version install-result cache so repeated snapshots in one session do not run the package version probe every time.
• Add a standalone helper APK install/capture smoke against a release-mode Android test app, separate from the existing Expo Go smoke.
• Investigate toast text capture/buffering, similar to mature Android automation stacks, if we hit real missed-toast scenarios.
• Investigate secondary-display support via Android multi-display APIs if a real provider/device scenario needs it.

Notes

Keep these incremental. The v1 helper should remain one-shot over am instrument with injected ADB transport; do not introduce a long-lived server unless a concrete workflow requires it.

[thymikee]

Closing this as PR #470 covers the immediate reliability/performance follow-ups: the Android snapshot helper install-result cache and release-mode helper smoke. Secondary-display support is split to #471. Toast capture/buffering is deferred until we have a concrete missed-toast workflow that needs transient UI event support.