Add OpenRouter LLM provider integration

[hellogreencow]

What?
This pull request implements OpenRouter support into JuliaOS, adding a new LLM provider option. The integration includes all necessary modules, tests, and configurations to allow JuliaOS to connect with OpenRouter's API for accessing various AI models.

Why?
OpenRouter provides a unified API to access multiple AI models including Anthropic Claude, GPT-4, Llama, and many others. This integration enhances JuliaOS's capabilities by:

• Expanding the available LLM model options for users
• Providing a fallback option if other providers have outages
• Creating a more flexible architecture that can leverage multiple model providers

How?
The implementation:

• Adds a new OpenRouter handler and client in the agents package
• Implements proper authentication with OpenRouter API
• Handles message formatting specific to OpenRouter requirements
• Integrates with the existing LLM provider framework in JuliaOS
• Includes proper error handling and response parsing

Testing?
All features have been thoroughly tested:

• Created and executed standalone tests to verify OpenRouter connectivity
• Verified proper API integration with test OpenRouter API keys
• Confirmed compatibility with the existing JuliaOS framework
• Validated handling of various response formats from different models

Technical Details

• API Authentication: Uses API key authentication with OpenRouter
• Response Format: Properly parses and handles JSON responses from OpenRouter
• Error Handling: Includes robust error handling for API failures
• Configuration: Provides necessary configuration options for OpenRouter endpoints

Future Considerations

• Add support for additional OpenRouter-specific features in future updates
• Consider implementing model-specific optimizations based on OpenRouter's available models
• Monitor performance and adjust timeouts/retry logic as needed