feat(compose): add enhanced tool interfaces with multimodal support

[zhuangjie1125]

Introduce EnhancedInvokableTool and EnhancedStreamableTool interfaces that support returning structured multimodal results (ToolResult) instead of plain strings.

Key changes:

1. New Tool Interfaces (components/tool/interface.go):

   • EnhancedInvokableTool: accepts ToolArgument, returns *ToolResult
   • EnhancedStreamableTool: accepts ToolArgument, returns StreamReader[*ToolResult]

2. Tool Utils (components/tool/utils/):

   • Added InferEnhancedTool and InferEnhancedStreamTool for type inference
   • Added NewEnhancedTool and NewEnhancedStreamTool factory functions
   • Support both regular and optionable variants

3. ToolsNode Enhancement (compose/tool_node.go):

   • Added EnhancedInvokableToolMiddleware and EnhancedStreamableToolMiddleware
   • Auto-conversion between enhanced invokable and streamable endpoints
   • Priority given to enhanced tools when both interfaces are implemented
   • Updated interrupt/rerun state to track enhanced tool results separately

4. Schema Extensions (schema/message.go):

   • Added ToolPartType enum (text, image, audio, video, file)
   • Added ToolArgument and ToolResult structs for structured I/O
   • Added ToolOutputPart with multimodal content support
   • Added ConcatToolResults for stream chunk merging
   • Added ToMessageInputParts() for ToolResult to Message conversion
   • Enhanced Message.String() to display multimodal content

5. React Agent Integration (flow/agent/react/):

   • Added enhanced tool result senders for MessageFuture
   • Added middleware support for enhanced tool result collection

This enables tools to return rich content like images, audio, video, and files alongside text, supporting advanced multimodal AI agent scenarios.

[codecov]

Codecov Report

❌ Patch coverage is 56.94864% with 285 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.47%. Comparing base (e328752) to head (49099bc).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
schema/message.go	56.69%	93 Missing and 30 partials ⚠️
compose/tool_node.go	77.43%	36 Missing and 15 partials ⚠️
components/tool/utils/invokable_func.go	0.00%	49 Missing ⚠️
components/tool/utils/streamable_func.go	54.34%	17 Missing and 4 partials ⚠️
flow/agent/react/react.go	9.09%	20 Missing ⚠️
flow/agent/react/option.go	45.16%	15 Missing and 2 partials ⚠️
components/tool/callback_extra.go	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #760      +/-   ##
==========================================
- Coverage   81.70%   80.47%   -1.23%     
==========================================
  Files         129      129              
  Lines       12427    13007     +580     
==========================================
+ Hits        10153    10468     +315     
- Misses       1518     1737     +219     
- Partials      756      802      +46     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.