Given an integer array `arr`, find the maximum score of a pair of indices `(i, j)` such that `0 <= i < j < arr.length`. The score of a pair is defined as: `score(i, j) = arr[i] + arr[j] + 2 * i - 3 * j` Return the maximum score among all valid pairs.
Explanation: For i = 0 and j = 2, the score is arr[0] + arr[2] + 2 * 0 - 3 * 2 = 8 + 5 + 0 - 6 = 7. No other pair has a higher score.
Explanation: For i = 0 and j = 1, the score is arr[0] + arr[1] + 2 * 0 - 3 * 1 = 1 + 10 + 0 - 3 = 8. Another pair (i = 1, j = 2) also gives a score of 10 + 2 + 2 - 6 = 8.