fix(OpenAI): support web search image results and settings

[e4se]

What:

• Bug Fix
• New Feature

Description:

Adds missing image search support to Responses API web search objects.

• Parse optional web_search_call.results entries into typed OutputWebSearchToolCallResult objects.
• Expose image URLs, source website URLs, thumbnails, and captions without dropping optional fields.
• Parse search_content_types and image_settings from WebSearchTool.
• Add typed support for max_results and caption image settings.
• Add fixtures and tests for complete and optional payloads.

See the OpenAI documentation: Image search results.

Tests:

• Unit test suite: 1,129 passed (5,109 assertions).
• Code style checks passed.

[iBotPeaches]

minor formatting, but otherwise looks good