Given a two dimensional grid consisting of $0$s (representing land) and $1$s (representing water), an island is a maximal group of $0$s connected horizontally or vertically.

A closed island is an island that is completely surrounded by $1$s on all four sides (top, bottom, left, and right), meaning it does not touch the boundary of the grid.

Return the total number of closed islands in the grid.

Constraints:

• $1 \leq$ grid.length, grid[0].length $\leq 100$

• $0 \leq$ grid[i][j] $\leq 1$

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