Enhance Hardhat etherscan configuration for multi-network support with ES6 syntax

[Copilot]

This PR modernizes and enhances the Hardhat configuration to support contract verification across multiple blockchain networks.

Changes Made

🔄 ES6 Module Conversion

• Converted hardhat.config.js from CommonJS to ES6 syntax to match the project's "type": "module" configuration
• Changed require() to import and module.exports to export default

🌐 Multi-Network Etherscan Support

Enhanced the etherscan configuration from a single API key to support multiple networks:

Before:

etherscan: {
  apiKey: process.env.ETHERSCAN_API_KEY,
}

After:

etherscan: {
  apiKey: {
    // Ethereum networks
    mainnet: process.env.ETHERSCAN_API_KEY,
    sepolia: process.env.ETHERSCAN_API_KEY,
    
    // Polygon networks
    polygon: process.env.POLYGONSCAN_API_KEY,
    polygonMumbai: process.env.POLYGONSCAN_API_KEY,
    
    // Arbitrum networks
    arbitrumOne: process.env.ARBISCAN_API_KEY,
    arbitrumSepolia: process.env.ARBISCAN_API_KEY,
    
    // BSC networks
    bsc: process.env.BSCSCAN_API_KEY,
    bscTestnet: process.env.BSCSCAN_API_KEY,
  },
}

➕ Additional Network Support

• Added Arbitrum network configuration that was previously missing
• Now supports deployment to: Ethereum, Polygon, Arbitrum, and BSC networks

📚 Documentation & Comments

• Added comprehensive environment variable documentation at the top of the file
• Added clear section comments throughout the configuration
• Documented all required API keys for each block explorer service

🔧 Environment Variables Required

The configuration now supports these environment variables for block explorer verification:

• ETHERSCAN_API_KEY - For Ethereum networks (mainnet, sepolia)
• POLYGONSCAN_API_KEY - For Polygon networks
• ARBISCAN_API_KEY - For Arbitrum networks
• BSCSCAN_API_KEY - For BSC networks

This enhancement enables seamless contract verification across all major EVM-compatible networks while maintaining clean, well-documented configuration code.

This pull request was created as a result of the following prompt from Copilot chat.

Restore and enhance the Hardhat etherscan configuration to support multiple networks. The etherscan section should use environment variables for API keys for each supported network (e.g., ETHERSCAN_API_KEY for Ethereum, POLYGONSCAN_API_KEY for Polygon, ARBISCAN_API_KEY for Arbitrum, BSCSCAN_API_KEY for BSC). The configuration should use 'export default' (ES6 style). Add code comments for clarity. Do not include actual API keys, just reference them via process.env. Document the environment variable requirements at the top of the file as a comment.

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[sonnyquinn24]

@copilot