This pull request adds the core functionality for a token swap DApp, allowing users to swap between native tokens (e.g., CORE) and ERC-20 tokens (USDT, USDC).
Users can perform swaps from CORE to USDC/USDT and between USDT and USDC.
It includes wallet connection via MetaMask, dynamic input/output calculations, and seamless transactions with a 0.5% fee.