Get Balances

There is a separate balance for each mint and each unit:

pub async fn mint_balances(multi_mint_wallet: &MultiMintWallet) -> Result<(), Error> {
    for wallet in multi_mint_wallet.get_wallets().await {
        let balance = wallet.total_balance().await?;
        let unit = wallet.unit;
        let mint_url = wallet.mint_url;

        println!("{mint_url}: {balance} {unit}");
    }

    Ok(())
}