Avoid contour computation when both features are the same on X and Y axis

[RaghavaAlajangi]

• If the features on both the X and Y axes are the same (e.g., index vs. index, or index vs. time), the resulting data will always be symmetrical along the diagonal line where X = Y. In many cases, this scenario is either meaningless or trivial.
• If the values are the same, every point will be on the diagonal, and there will be no useful contours to draw.

Advantages:

• Computational efficiency
• Shapeout2 optimization