Bound SQLite integrity checks for diagnostic attachments (#40688)

## Why

Diagnostic uploads skip the doctor attachment if report generation exceeds its
overall timeout. SQLite integrity scans can be delayed by large databases or
lock contention.

## What changed

- Give each database integrity scan a one-second deadline when collecting a
  diagnostic attachment.
- Interrupt scans and lock waits at the deadline, preserve any corruption rows
  already returned, and report an incomplete clean scan as a warning.
- Keep direct `codex doctor` integrity checks unbounded.

## Testing

- Cover interrupted scans, lock waits, retries without a deadline, and
  corruption results returned before interruption.

GitOrigin-RevId: 4817fb459ac53953669a9ba5f03397a6fc82c72e