[WIP]: Experimentally use Viem in OpStack finalizer

[nicholaspai]

Currently showing my WIP trying to use the Viem client to support limited finalizer functionality:

• check withdrawal status
• build proveWithdrawalTransaction and finalizeWithdrawal args

Current limitations of Viem:

• No easy way to convert ethers Provider to Viem transport, meaning that RPC calls won't go through our custom RetryProvider. The Viem transport does have retry and fallback logic natively but not caching built-in. I think we'll need a larger refactor to support this migration if we wanted to use Viem more widely throughout the codebase. We can probably get away with Viem in the finalizer if we restrict its use only for the few RPC calls required to support finalizer functions (e.g. building transaction args requires querying contracts)
• getWithdrawalStatus only supports querying a transaction with a single withdrawal. This isn't very useful for us today since we usually multicall our withdrawals. We need something like this PR in order to use Viem to finalize
• Viem accounts don't seem to be obviously interoperable with ethers Signers

Suggested roadmap

• Use Viem for optimism mainnet, and then a few op stack chains over time.
• Build generalized Viem modules that could help us install viem into the broader codebase like:
  • converting between Ethers providers/signers and Viem transports/accounts

Resources

• viem.sh/op-stack docs
• github