feat/withdrawals execution layer spec

[4rgon4ut]

This PR addresses implementation of WithdrawalsExecutionLayerSpec along with specs responsibility separation.
Current WithdrawalsBaseSpec include only protocol level checks to make sure shanghai is activated and withdrawals are applied and executed correctly as system operations.
Other checks like claims execution, balance change and transfer events ERC20 consistency lies in the WithdrawalsExecutionLayerSpec scope.

Changes:

• Fixed execution layer events and ERC20 balance checks
• Execution layer logic removed from the WithdrawalsBaseSpec and added to WithdrawalsExecutionLayerSpec to separate specs responsibility
• New functions added to libgno to interact with a smart contracts
• Little refactoring and cleanup in withdrawals/test.go