Fix arbsepolia verify

[aelmanaa]

This pull request makes several improvements to the Hardhat configuration for the CCIP project, focusing on type safety, network configuration robustness, and dependency updates. The most notable changes include adding fallback URLs for network RPC endpoints, introducing type-safe conversion for network configs, fixing a bug in chain descriptors for Arbitrum Sepolia, and updating dependencies.

Configuration robustness and type safety:

• Added fallback default URLs for all EVM testnet RPC endpoints in networks.ts, preventing runtime errors if environment variables are missing.
• Introduced a type adapter and conversion function (HardhatNetworks and toHardhatNetworks) in hardhat.config.ts to ensure network configurations are type-safe and compatible with Hardhat’s expected structure.
• Updated the way networks are passed to Hardhat, using the new type-safe conversion instead of a loose type cast.

Chain descriptor and verification fixes:

• Added a custom chain descriptor for Arbitrum Sepolia in hardhat.config.ts to fix a bug with hardhat-verify, ensuring proper explorer integration and verification.

Dependency updates:

• Upgraded hardhat and @nomicfoundation/hardhat-errors to the latest versions and added @types/bn.js to dev dependencies in both package.json and package-lock.json. [1] [2] [3] [4] [5]

These changes collectively improve the reliability, maintainability, and compatibility of the Hardhat setup for development and deployment.

[github-actions]

👋 aelmanaa, thanks for creating this pull request!

To help reviewers, please consider creating future PRs as drafts first. This allows you to self-review and make any final changes before notifying the team.

Once you're ready, you can mark it as "Ready for review" to request feedback. Thanks!