Maximum Frequency Stack

Design a stack-like data structure that pushes elements and pops the **most frequent** element. If there is a tie for the most frequent element, the element closest to the top of the stack is popped. Implement the following operations: - `push(val)` - pushes an integer `val` onto the stack. - `pop()` - removes and returns the most frequent element in the stack. If there is a tie, the element closest to the stack top is removed. **Input format:** An array of commands where each command is either `["push", val]` or `["pop"]`. Return an array of results where `push` produces `null` and `pop` produces the popped value.