Function calculate_maker_taker_commission 

pub fn calculate_maker_taker_commission(
    instrument: &InstrumentAny,
    last_qty: Quantity,
    last_px: Price,
    fee_rate: Decimal,
    use_quote_for_inverse: Option<bool>,
) -> Result<Money>

Calculates maker/taker commission from an explicitly resolved fee rate.

This is the single shared arithmetic for notional-based maker/taker fees used by both account calculations and execution fee models. Contract terms (notional and currency) come from the instrument; fee policy (the rate) comes from the account-owned schedule and must already be resolved by the caller.

The fee rate alone decides the commission sign: a positive rate charges and a negative rate rebates, including at a negative price.

Errors

Returns an error if the notional value cannot be calculated, arithmetic overflows, or the commission cannot be represented in the notional currency.