Function resolve_indexed_colour_map_full 

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

Resolve an IfcIndexedColourMap to its palette + per-triangle indices.

Schema (IFC4):

• attr 0: MappedTo → IfcTessellatedFaceSet
• attr 1: Opacity (optional 0..=1, 1.0 when omitted)
• attr 2: Colours → IfcColourRgbList (attr 0 = ColourList)
• attr 3: ColourIndex → 1-based palette index per triangle