Add telemetry module with tracing (agent/tool/llm/pipeline_step spans),
metrics (5 histograms/counters), and setup with optional OTLP exporters.
Uses no-op pattern when opentelemetry not installed. GenAI Semantic
Conventions for LLM spans. Integrated into ReactEngine, LLMGateway,
ToolBase, and FastAPI app.
- WenxinProvider: Baidu ERNIE via Qianfan v2 OpenAI-compatible API, AK/SK token auth
- DoubaoProvider: ByteDance Doubao via Volcengine Ark API
- YuanbaoProvider: Tencent Hunyuan via OpenAI-compatible API with enhancement mode
- All inherit from OpenAICompatibleProvider for retry/circuit breaker support
- 16 tests passing