Support `enums` inside `structs` and `structs` inside `enums` in the ABIgen about fuels-rs HOT 1 CLOSED

For my work with the stdlib, the most common cases of using nested types like this are going to be Results & Options.

For the Result type, this is a common usage I need to be able to handle:

pub enum Sender {
    Address: Address,
    ContractId: ContractId,
}
pub enum AuthError {
    InputsNotAllOwnedBySameAddress: (),
}

pub fn msg_sender() -> Result<Sender, AuthError>

I want to be able to have abi functions return the result from the msg_sender() function.
Tecnically, the Resultin this case is an Enum which contains an Enum which contains a Struct

from fuels-rs.