Max Area of Island

Implement max_area_of_island(grid) -> int.

grid is a list of rows of integers, 1 for land and 0 for water. Land cells that touch up, down, left or right belong to the same island, and an island's area is its number of cells. Return the largest area, or 0 if there's no land at all.

max_area_of_island([
    [1, 1, 0, 0, 1],
    [0, 1, 0, 1, 1],
    [0, 0, 0, 0, 1],
    [1, 0, 1, 0, 0],
])
# 4   (the island on the right: (0,4), (1,3), (1,4), (2,4))

Grids go up to 300×300 and may be entirely land, so aim for O(rows·cols) and avoid deep recursion (Python's default limit is about 1,000 frames). You may modify grid.