Factory function to create the appropriate SmoothTrace instance based on layer data.
Violin KDE traces are no longer created here — they use TraceType.VIOLIN_KDE and are handled directly by TraceFactory.
The MAIDR layer data for the smooth trace
A SmoothTrace instance: - SmoothTraceSvgXY if the data contains svg_x/svg_y coordinates - SmoothTrace otherwise (standard smooth/regression line)
Factory function to create the appropriate SmoothTrace instance based on layer data.
Violin KDE traces are no longer created here — they use TraceType.VIOLIN_KDE and are handled directly by TraceFactory.