Update 4337 SafeOperationResponse types to match backend changes

[yagopv]

Context / issue

Backend is going to update types in the 4337 endpoints

safe-global/safe-transaction-service#2361

All these typed will be strings

    nonce = Uint256Field()
    call_gas_limit = Uint256Field()
    verification_gas_limit = Uint256Field()
    pre_verification_gas = Uint256Field()
    max_fee_per_gas = Uint256Field()
    max_priority_fee_per_gas = Uint256Field()

Proposed solution

Review the API kit and starter kit to ensure everything is working correctly. Make any necessary updates.