Given an `m x n` `matrix`, return `true` if the matrix is Toeplitz. Otherwise, return `false`.

A matrix is Toeplitz if every diagonal from top-left to bottom-right has the same elements.

Example 1:

    Input: matrix = [[1,2,3,4],[5,1,2,3],[9,5,1,2]]
    Output: true
    Explanation:
    In the above grid, the diagonals are:
    "[9]", "[5, 5]", "[1, 1, 1]", "[2, 2, 2]", "[3, 3]", "[4]".
    In each diagonal all elements are the same, so the answer is True.

Example 2:

    Input: matrix = [[1,2],[2,2]]
    Output: false
    Explanation:
    The diagonal "[1, 2]" has different elements.

Constraints:

- `m == matrix.length`
- `n == matrix[i].length`
- `1 <= m, n <= 20`
- `0 <= matrix[i][j] <= 99`

Follow up:

- What if the `matrix` is stored on disk, and the memory is limited such that you can only load at most one row of the matrix into the memory at once?
- What if the `matrix` is so large that you can only load up a partial row into the memory at once?