Function instrument_taker_fee 

pub fn instrument_taker_fee(instrument: &InstrumentAny) -> Decimal

Returns the effective taker fee rate for a Polymarket instrument.

Polymarket sets this from the Gamma market’s feeSchedule.rate. When the feeSchedule is unavailable (e.g. CLOB-only flow) the instrument’s taker fee defaults to zero and no commission is charged.