Function create_inferred_fill_for_qty 

pub fn create_inferred_fill_for_qty(
    order: &OrderAny,
    report: &OrderStatusReport,
    account_id: &AccountId,
    instrument: &InstrumentAny,
    fill_qty: Quantity,
    ts_now: UnixNanos,
) -> Option<OrderEventAny>

Creates an inferred fill with a specific quantity.

Unlike create_incremental_inferred_fill, this takes the fill quantity directly rather than calculating it from order state. Useful when order state hasn’t been updated yet (e.g., during external order processing).