fix(images): add optional content_filter_results to Image model + test coverage

[lucasalencarxisto-stack]

Context

The Images API may return additional metadata such as content_filter_results
(for categories like sexual_minors, violence, etc.). This field was missing
from the current Image model in the SDK, causing a mismatch between the API
payload and the SDK types.

Changes

• Added content_filter_results: Optional[Dict[str, Any]] to Image model.
• Created a new test (tests/test_images_missing_fields.py) that mocks the
  API response with revised_prompt and content_filter_results and asserts
  that the SDK parses them correctly.

Why

This change ensures the SDK fully reflects the Images API payload and avoids
loss of safety-related metadata. It also improves test coverage for optional
fields that the API may include.

[lucasalencarxisto-stack]

Hi OpenAI team 👋

This PR addresses an issue where the content_filter_results field, which is
sometimes returned by the Images API, was not present in the SDK Image model.
I added this optional field and included a dedicated test to confirm it is
properly handled.

Let me know if you’d like me to extend the test with more categories or add
docs coverage. Thanks for reviewing 🚀

[lucasalencarxisto-stack]

Hi team 👋

This PR is focused and ready:

• Marks content_filter_results as optional in Image responses.
• Adds tests for both presence and absence.
• No runtime changes, just typing + coverage.

I believe this is a good candidate for a quick merge since it improves developer experience with minimal surface area. Happy to rebase or adjust if needed. 🚀