// Rotate Image — MEDIUM
// Category: array
You are given an `n x n` 2D matrix representing an image. Rotate the matrix **90 degrees clockwise**, **in-place**.
Do not allocate another 2D matrix — modify the input matrix directly.
Example: matrix = [[1,2,3],[4,5,6],[7,8,9]]
Output: [[7,4,1],[8,5,2],[9,6,3]]