wip: Support registering external smart contracts

[alex-stone]

What changed? Why?

This starts to add support for registering external smart contracts
with CDP.

This will enable developers to use these register smart contracts
to invoke, read, and create webhooks associated with the contract!

Testing

# Deploy a token and get an ERC20 ABI ref
smart_contract = wallet.deploy_token(name: "Test Coin", symbol: "TEST", total_supply: 1000)
smart_contract.wait!

asset = Coinbase::Asset.fetch(:base_sepolia, :usdc)

# Register an external contract w/ a known ABI
external_contract = Coinbase::SmartContract.register(
  network: Coinbase::Network::BASE_SEPOLIA,
  contract_address: asset.address_id,
  name: "USDC YO",
  abi: smart_contract.abi
)

Qualified Impact

[cb-heimdall]

🟡 Heimdall Review Status

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