Function apply_fee_payment 

pub(crate) async fn apply_fee_payment<N, P>(
    sponsor: Option<&TempoSponsor>,
    provider: Option<&P>,
    chain: Chain,
    tx: &mut N::TransactionRequest,
    payer: Address,
) -> Result<()>
where
    N: Network,
    N::TransactionRequest: Default + FoundryTransactionBuilder<N>,
    P: Provider<N>,

Attaches the fee payment to a built transaction: the sponsor signature when a sponsor is configured, otherwise the resolved fee token for payer (printing it when it was resolved).