feat: add Mantle and MantleTestnet to EthereumNetworks enum

[skydudie]

This pull request adds support for the Mantle mainnet and testnet Ethereum networks throughout the codebase. The changes ensure that Mantle networks (netId 5000 and 5003) are recognized and properly handled in both the core logic and the test suite.

Mantle network support:

• Added mantle (netId 5000) and mantleTestnet (netId 5003) to the EthereumNetworks enum in dnsTxt.ts, enabling recognition of these networks in the application logic.
• Updated the EthereumNetworkIdT union type to include Mantle mainnet and testnet, ensuring type safety and validation for these new network IDs.

Testing enhancements:

• Added unit tests in index.test.ts to verify that Mantle mainnet and testnet records are accepted by parseDocumentStoreResults.
• Added a new Astron record to the expected results in the getDocumentStoreRecords for Astron test, likely to ensure comprehensive coverage for multiple networks.