Signs an Add message using the account's signTypedData method.
const signedMessage = await signAdd({ account: yourAccount, message: yourAddMessage,});
function signAdd(options: SignAddOptions): Promise<Hex>;
The options for signing the Add message.
let options: { account: Account; message: AddMessage };
let returnType: `0x${string}`;
A promise that resolves to the signature of the Add message.