Retry transient empty native accessibility snapshots after tap

[DjDeveloperr]

Summary

• Added retry logic to native accessibility snapshot capture so transient empty trees are retried before being returned.
• Treats empty roots and zero-sized leaf roots as transient failures, with up to 10 attempts and a 100ms delay between retries.
• Covers the describe path used by --source native-ax, daemon auto fallback, and direct native accessibility snapshots.
• Added unit tests for both empty and usable snapshot shapes.

Testing

• cargo fmt --manifest-path server/Cargo.toml --check
• cargo test --manifest-path server/Cargo.toml native::bridge::tests -- --nocapture