What is the fastest and most space-efficient way to sort a 2d array with sorted rows:

Input:

[
  [2, 3, 5, 6],
  [1, 5, 7],
  [2, 3, 4, 9],
  [2, 3, 4],
]

Output:

[
  [1, 5, 7],
  [2, 3, 4],
  [2, 3, 4, 9],
  [2, 3, 5, 6],
]

Note: this is not the same question as Most efficient way to sort a 2d array with sorted rows into 1d sorted array