v2.0.0 - 完整 Anthropic 协议支持

v2.0: Full tool calls, thinking, and streaming support

Request mapping (Anthropic -> OpenAI):
- tools: input_schema -> function.parameters
- tool_choice: auto/any/tool -> auto/required/specific
- tool_result content blocks -> role:tool messages
- tool_use in assistant messages -> tool_calls
- thinking param -> chat_template_kwargs.enable_thinking
- top_k passthrough

Response mapping (OpenAI -> Anthropic):
- Non-streaming: reasoning_content -> thinking block, tool_calls -> tool_use blocks
- Streaming: block state machine (thinking -> text -> tool_use) with proper
  content_block_start/stop transitions and event types
- Streaming tool_calls: input_json_delta with partial_json
- Streaming thinking: thinking_delta events
- message_delta includes input_tokens + output_tokens