test: Enhance o3-pro test to verify model metadata and response parsing

- Add verification that o3-pro model was actually used (not just requested)
- Verify model_used and provider_used metadata fields are populated
- Add graceful handling for error responses in test
- Improve test documentation explaining what's being verified
- Confirm response parsing uses output_text field correctly

This ensures the test properly validates both that:
1. The o3-pro model was selected and used via the /v1/responses endpoint
2. The response metadata correctly identifies the model and provider

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

tests/test_pii_sanitizer.py

@@ -3,7 +3,7 @@
 
 import unittest
 
-from tests.pii_sanitizer import PIIPattern, PIISanitizer
+from .pii_sanitizer import PIIPattern, PIISanitizer
 
 
 class TestPIISanitizer(unittest.TestCase):