fix: address PR review comments for arrow-rs migration
- Use delimiter.into_iter() directly instead of boxed iterators
- Collect directly into Utf8Array without intermediate Vec
- Use arr.into_iter() in create_iter() to avoid Vec allocation
- Remove DaftResult return from create_iter() since no fallible ops
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>