Add PatchedChatStepFun adapter for StepFun reasoning models (step-3.7-flash,
step-3.5-flash). Captures reasoning from both streaming and non-streaming
responses and replays it on historical assistant messages for multi-turn
tool-call conversations.
- New: PatchedChatStepFun adapter with streaming/non-streaming reasoning capture
- Support both reasoning and reasoning_content field names
- 17 unit tests covering all response paths
- Updated: config.example.yaml with StepFun configuration example