EVM Contract Fetcher

This tool retrieves verified Solidity contract source code and metadata for a given EVM contract address via a multi-strategy lookup. It accepts chain_id (integer EVM chain ID), contract_address (0x-prefixed contract address), and explorer_api_key (optional block explorer API key used only as a fallback when Sourcify has no result). The implementation first uses the public Sourcify repository, then, if enabled by explorer_api_key, the matching Etherscan-style block explorer API. It returns structured data such as source files, ABI, compiler version, optimization settings, or a structured error when verification data cannot be found. All JSON output must strictly validate against the system-provided structured output schema for this tool.