Implement parallel tool execution in AgentLoop, following the approach
used in Nanobot (_partition_tool_batches) and Zeroclaw (parallel_tools).
Key changes:
- partition_tool_batches(): group tool calls into batches based on
concurrency_safe flag. Safe tools run in parallel via join_all;
exclusive tools (e.g. bash) run in their own sequential batch.
- execute_tools(): now uses batching instead of flat sequential loop.
- CalculatorTool: add read_only() -> true so it participates in
parallel batches (it has no side effects, so concurrency_safe = true).
4 unit tests added covering: mixed safe/exclusive, all-safe single
batch, all-exclusive separate batches, unknown tool defaults.
- 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.
