Function epic_wallet_rust_lib::get_wallet_secret_key_pair

pub fn get_wallet_secret_key_pair(
    wallet: &Arc<Mutex<Box<dyn WalletInst<'static, DefaultLCProvider<'static, HTTPNodeClient, ExtKeychain>, HTTPNodeClient, ExtKeychain>>>>, 
    keychain_mask: Option<SecretKey>, 
    index: u32
) -> Result<(SecretKey, PublicKey), Error>