Save declared class only if the fee charge was successful

[juanbono]

Declare and Declare V2 transactions charge a fee after we save the ContractClass in the State.
This is a problem because when the transaction's sender doesn't have enough balance, the transaction fails, but the cached state remains with the already added entry (class_hash, contract_class).

We should check the return of the charge_fee method and only save it into the state when it finishes successfully.