Add ERC-20 Token Support

[devin-ai-integration[bot]]

This pull request adds support for ERC-20 tokens, including functionality for sending tokens, approving tokens, fetching token metadata, and checking token approval requirements. The implementation aligns with ethers v6 library's API and ERC-20 standards. The test suite has been updated to handle expected errors and is passing as intended. Please review the changes and provide feedback.