Given an array of integers heights representing a histogram's bar height where the width of each bar is 1, find the area of the largest rectangle in the histogram.
- An array of integers
heights.
Input: heights = [2, 1, 5, 6, 2, 3]
Output: 10
Explanation: The largest rectangle is formed by the bars with heights 5 and 6, with width 2.
Area = 5 * 2 = 10.