Perform matrix Candy Crush elimination

##### Question Implement a function that, given an m × n integer matrix representing colored blocks (same integers = same color), performs one round of "Candy-Crush" elimination: A cell is removed (set to 0) if at least two of its four neighbors (up, down, left, right) share the same color as the cell. After removals, all remaining non-zero cells in each column fall down to fill empty spaces; zeros rise to the top. Return the resulting matrix after this single round.