Resolve strict Clippy findings across all targets, preserve public API compatibility with scoped lint exceptions, and fix sourced messages retaining media references. Replace meval and its future-incompatible nom dependency with a bounded internal expression parser and regression tests.
- 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.
