DeepSeek's thinking mode requires both:
- extra_body.thinking.type: "enabled" to activate thinking mode
- top-level reasoning_effort: "max" or "high" to control depth
Previously, the ChatCompletionsTransport only handled Kimi's thinking
mode — DeepSeek was left unmapped, so reasoning_effort config was
silently dropped.
This patch:
1. Adds is_deepseek: bool to the Params dataclass, detected by
base_url matching api.deepseek.com
2. Maps Hermes effort levels (xhigh/max → "max", low/medium/high →
themselves) to the top-level reasoning_effort parameter
3. Sets extra_body.thinking.type alongside the effort
4. Strips reasoning_content from assistant messages sent back to
DeepSeek, preventing 400 errors when thinking was enabled
068c24f8a4