Function instrument_fee_exponent 

pub fn instrument_fee_exponent(instrument: &InstrumentAny) -> f64

Returns the fee-schedule exponent for a Polymarket instrument. Polymarket stores feeSchedule.exponent in the instrument’s info map at parse time. Defaults to 1.0 when missing so the fee curve degenerates to the simple fee = C * rate * p * (1 - p) form used by compute_commission.