Resolve merge conflicts in o3-pro response parsing fix

- Use new output_text field format for o3-pro responses
- Update test expectations to use resolved model name o3-pro-2025-06-10
- Keep HTTP transport recorder and PII sanitization improvements
- Preserve both bug fix and recent GPT-5 updates

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

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

providers/registry.py

@@ -351,6 +351,17 @@ class ModelProviderRegistry:
         instance = cls()
         instance._initialized_providers.clear()
 
+    @classmethod
+    def reset_for_testing(cls) -> None:
+        """Reset the registry to a clean state for testing.
+
+        This provides a safe, public API for tests to clean up registry state
+        without directly manipulating private attributes.
+        """
+        cls._instance = None
+        if hasattr(cls, "_providers"):
+            cls._providers = {}
+
     @classmethod
     def unregister_provider(cls, provider_type: ProviderType) -> None:
         """Unregister a provider (mainly for testing)."""