Function calculate_colr_transform 

fn calculate_colr_transform(metrics: &ColrMetrics) -> Affine

Calculate transform for COLR glyphs.

This uses pre-calculated metrics to compute the final positioning transform for a COLR glyph, taking into account:

• Y-axis flip (fonts use upside-down coordinate system)
• Scale compensation (to avoid double-application of run transform scale)
• Bounding box alignment