Improve Twitter Agent Implementation

[spacexbt]

This PR improves the Twitter agent implementation by:

1. Modularizing the code into separate components:

   • exceptions.py - Custom exceptions
   • models.py - Data models and types
   • cache.py - Caching functionality
   • request_handling.py - Async request handling
   • agent.py - Main agent implementation

2. Adding new features:

   • Improved error handling with custom exceptions
   • Async/await support for better performance
   • Request retry logic with exponential backoff
   • Rate limit handling
   • Result caching with TTL
   • Configuration validation
   • Comprehensive logging

3. Improving code quality:

   • Better type hints
   • More modular and maintainable structure
   • Separation of concerns
   • Improved error messages
   • Better validation of inputs

The changes make the code more robust, maintainable, and performant while adding important features for production use.