## What this fixes
Closes#16400.
`get_data_openai()` currently returns `created: null` when callers do
not pass a timestamp, and it replaces explicit timestamp values with the
current time. This makes non-streaming OpenAI-compatible responses
inconsistent with the expected integer `created` timestamp field.
## Change
- Preserve explicit `created` values when provided.
- Default non-streaming responses to `int(time.time())` when `created`
is not provided.
- Add focused unit coverage for default timestamps, explicit timestamps,
and unchanged streaming chunk shape.
## Verification
- `./.venv/bin/python -m pytest
test/unit_test/api/utils/test_api_utils.py -q`
- `python3 -m py_compile api/utils/api_utils.py
test/unit_test/api/utils/test_api_utils.py`
- `uvx ruff check api/utils/api_utils.py
test/unit_test/api/utils/test_api_utils.py`
---------
Co-authored-by: Harsh Kashyap <harshkashyap@Harshs-MacBook-Pro.local>
