Implement WeatherTool using Open-Meteo API

[IreneXY]

Summary

• Add WeatherTool as cross-platform built-in example tool in core
• Uses Open-Meteo geocoding API with count=5 (returns multiple matches for city disambiguation)
• Returns raw JSON from both geocoding and weather APIs, letting LLM interpret and format
• No API key required, pure HTTP — works on all platforms
• Injectable http.Client for testing
• Place in toolbox/ directory (separate from tool/ which holds interface definitions)

Directory structure

chat_core/lib/src/
├── tool/        # Interface definitions (Tool, ToolRegistry)
└── toolbox/     # Concrete tool implementations (WeatherTool)

Test plan

• dart analyze passes
• dart format --set-exit-if-changed . passes
• dart test — 63 tests passed (4 new unit + 1 integration)
• Integration test: LLM calls weather tool for "San Jose", disambiguates California from Costa Rica

🤖 Generated with Claude Code

Co-Authored-By: Claude Code noreply@anthropic.com