Best Focus Span
`heights` lists a daily focus score for each day, in order. Choose two different days i and j (i < j) to maximize `min(heights[i], heights[j]) * (j - i)` — think of it as the largest rectangle you could draw between two focus bars. Return that maximum value.
`heights` lists a daily focus score for each day, in order. Choose two different days i and j (i < j) to maximize `min(heights[i], heights[j]) * (j - i)` — think of it as the largest rectangle you could draw between two focus bars. Return that maximum value.
