Function simplify_element 

pub fn simplify_element(
    records: &[SimplifyRecordInput<'_>],
    level: u8,
    rtc_offset: [f64; 3],
    unit_scale: f64,
    y_up: bool,
) -> Result<SimplifiedElement, SimplifySkip>

Simplify one element from its already-produced mesh records at the given demesher level (see SimplifyOptions::for_level).

unit_scale is metres per project length unit (the prepass/export unit scale); rtc_offset is the model origin shift in IFC Z-up metres.