feature: Chat Model Interfaces and Response Types Implementation

[xerial]

Chat Model Interfaces and Response Types Implementation

This PR introduces foundational interfaces for chat-based AI models along with new response types for error handling:

1. ChatModel: Basic interface for synchronous chat communication with properly defined return type
2. StreamingChatModel: Interface for streaming chat responses
3. StreamingChatResponseHandler: Callback interface for handling streaming responses with three event methods:
   • onPartialResponse: Receives incremental text updates
   • onComplete: Called when a full response is ready
   • onError: Provides error handling
4. ChatResponse: Response type for chat interactions with status code and content
5. Integration with StatusCode for proper error handling and reporting

These interfaces establish the core abstraction layer for implementing various chat model providers while offering both synchronous and streaming interaction patterns with standardized error handling capabilities.