Replace Etherscan ABI lookups with Sourcify

[0237h]

Etherscan requires an API key for ABI lookup and other operations.
Sourcify (https://sourcify.dev) is an open-source decentralized alternative.

This PR is still a draft:

• The conversion of network values to Sourcify chainID can fail for names that don't match Chainlist's format. See getSourcifyChainId.
• There are still instances where the Etherscan API is required such as the fetching of the startBlock (the next step after ABI fetching for init). This feature needs to fetch the contract creation hash which Sourcify doesn't provide through their API. See getStartBlockForContract which calls fetchDeployContractTransactionFromEtherscan and getContractNameForAddress which calls fetchSourceCodeFromEtherscan.

Aims to fix #1702, #1001.

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Latest commit: 46af177

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