OpenAI file uploads are eventually consistent — a freshly uploaded file
may briefly 404 from `retrieve` and is rejected by the fine-tuning
endpoint with `'file-... does not exist'` until processing finishes.
The async fine-tuning test called `acreate_fine_tuning_job` immediately
after `acreate_file` and flaked on this race.
Add a polling helper that waits up to ~30s for `status=processed` (and
short-circuits on `error`), called between upload and FT job creation.
Mirrors the same propagation lag covered by the `await asyncio.sleep(1)`
in the sister batches test, but more robust against longer delays.
Yuneng Jiang
a64716ed5b