Improve Ogmios-Kupo Backend Queries and VyFi DEX Integration

[bhatt-deep]

This PR enhances the Ogmios Backend pool utxos queries and VyFi DEX integration and improves overall code quality across multiple files. Key changes include:

VyFi DEX Enhancements (src/charli3_dendrite/dexs/amm/vyfi.py)

• Refactored VyFiCPPState class for better performance and maintainability
• Implemented asset-based pool selection
• Improved pools refresh mechanism with error handling

Backend Improvements (src/charli3_dendrite/backend/ogmios_kupo/__init__.py)

• Updated get_pool_utxos and get_pool_in_tx methods to use payment credentials
• Improved handling of asset filtering in Kupo requests

Example Script Updates (example.py)

• Added support for multiple DEX implementations