You're given an n x n 2D matrix representing an image. Rotate it 90 degrees clockwise, in place, and return it.
Transpose the matrix (flip across the main diagonal), then reverse each row — two simple operations that together produce a clockwise rotation without any extra matrix.
Example
Input: matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
Output: [[7, 4, 1], [8, 5, 2], [9, 6, 3]]