You are given an `m x n` grid (matrix) of integers `grid`, where `m >= 1` and `n >= 1`. A **path** in the matrix is a sequence of cells where: - You may move from a cell only to one of its 4 neighbors: up, down, left, or right (no diagonals). - Each step must go to a cell with a **strictly larger** value than the current cell. The length of a path is the number of cells in the path. **Task** Return the length of the **longest** strictly increasing path that can be found in the matrix. You may start the path at any cell. **Example** For example, given: - `grid = [[9, 9, 4], [6, 6, 8], [2, 1, 1]]` One of the longest increasing paths is `1 → 2 → 6 → 9`, so the answer is `4`. **Constraints** - `1 <= m, n <= 200` - `-10^9 <= grid[i][j] <= 10^9` Your solution should be efficient enough to handle the largest inputs within typical interview time limits.