Byte index slicing like `&text[..100.min(text.len())]` panics when the
byte index falls inside a multi-byte UTF-8 character (e.g., Chinese).
Changed to `text.chars().take(100).collect::<String>()` for safe
character-based truncation.
- Added ContentBlock enum for multimodal content representation (text, image).
- Enhanced ChatMessage struct to include media references.
- Updated InboundMessage and OutboundMessage to use MediaItem for media handling.
- Implemented media download and upload functionality in FeishuChannel.
- Modified message processing in the gateway to handle media items.
- Improved logging for message processing and media handling in debug mode.
- Refactored message serialization for LLM providers to support content blocks.
- Introduced a new CalculatorTool for performing various arithmetic and statistical calculations.
- Enhanced the AgentLoop to support tool execution, including handling tool calls in the process flow.
- Updated ChatMessage structure to include optional fields for tool call identification and names.
- Modified the Session and SessionManager to manage tool registrations and pass them to agents.
- Updated the OpenAIProvider to serialize tool-related message fields.
- Added a ToolRegistry for managing multiple tools and their definitions.
- Implemented tests for the CalculatorTool to ensure functionality and correctness.
