test: Enhanced test coverage for OpenAiRuntimeHintsTests

[alxkm]

Enhanced test coverage for OpenAiRuntimeHintsTests
Added comprehensive test cases to improve coverage of the OpenAiRuntimeHints class:

• Test infrastructure: Added @BeforeEach setup for better test isolation
• ClassLoader scenarios: Tests with null and custom ClassLoaders
• Member category validation: Ensures all MemberCategory values are registered for OpenAI types
• Idempotency testing: Verifies multiple registration calls don't create duplicates
• OpenAI-specific validation: Tests for API classes, audio/image APIs, and chat options registration
• Type categorization tests: Separate validation for enum types and nested classes
• Edge case coverage: Empty state validation and utility method testing

Key improvements include:

• Added specific tests for enum types (TtsModel, WhisperModel, ChatCompletionFinishReason, OutputModality)
• Added tests for nested classes (FunctionTool, FunctionTool.Function)
• Enhanced validation of OpenAI-specific API classes
• Comprehensive coverage of different ClassLoader scenarios

These additions ensure robust AOT hint registration behavior for OpenAI integration across different scenarios and improve overall test reliability.

[sobychacko]

Merged via 2dcc29a.