Function locate_axis_curve 

pub fn locate_axis_curve(
    entity: &DecodedEntity,
    decoder: &mut EntityDecoder<'_>,
) -> Option<DecodedEntity>

Resolve an IfcAlignment’s directrix curve.

IFC4X1 puts Axis at attribute 7; some publishers reuse Representation (6) or hang it at 8. Accept the first ref that resolves to an IfcAlignmentCurve or IfcPolyline (the curves AlignmentCurve::parse understands). A ref that fails to resolve is skipped, not fatal. Otherwise IFC4x3 Representation (attr 6) supplies the 'Axis' shape representation’s curve (IfcGradientCurve; an IfcSegmentedReferenceCurve contributes its gradient BaseCurve), or the 'FootPrint' 2D curve. None when neither path yields a curve.