Update `run()` to take `cancel_flag: Arc<AtomicBool>` that the worker threads will periodically check to see if it is `true`, exiting early (and returning empty results) if so.
Caller no longer needs to clone a `PathBuf`: can just pass `&Path`.
--- [//]: # (BEGIN SAPLING FOOTER) Stack created with [Sapling](https://sapling-scm.com). Best reviewed with [ReviewStack](https://reviewstack.dev/openai/codex/pull/1400). * #1401 * __->__ #1400
Standalone fuzzy filename search library that should be helpful in addressing https://github.com/openai/codex/issues/1261.