 * Given the coordinates of two rectilinear rectangles in a 2D plane, return the total area covered by the two
 * rectangles.
 *
 * The first rectangle is defined by its bottom-left corner (ax1, ay1) and its top-right corner (ax2, ay2).
 * The second rectangle is defined by its bottom-left corner (bx1, by1) and its top-right corner (bx2, by2).
 *
 * Example 1:
 * Rectangle Area