- Introduced `using_api` attribute in xAI auth for toggling between official API and CLI chat-proxy paths.
- Updated `xaiChatBaseURL` and `applyXAIChatHeaders` to conditionally apply the appropriate logic based on the `using_api` value.
- Added robust handling of attribute and metadata parsing for `using_api`.
- Extended test suite to cover `using_api` scenarios, including defaults, overrides, and header behaviors.