Function update_fee_fill_caches 

pub fn update_fee_fill_caches(
    msg: &OKXOrderMsg,
    instrument: &InstrumentAny,
    fee_cache: &mut FeeCache,
    filled_qty_cache: &mut FilledQtyCache,
)

Updates fee and fill caches from a raw OKX order message.

Call after parsing each message so subsequent messages in the same batch see the correct cumulative fee and filled quantity.