Given an array of integers ~heights~ representing the histogram's bar height where the width of each bar is ~1~, return /the area of the largest rectangle in the histogram/.
*Example 1:*
#+begin_src
Input: heights = [2,1,5,6,2,3]
Output: 10
Explanation: The above is a histogram where width of each bar is 1.
The largest rectangle is shown in the red area, which has an area = 10 units.