Lit Clusters
`grid` is a 2D pixel grid of 0s and 1s, where 1 means a lit pixel. Two lit pixels belong to the same cluster if they are adjacent horizontally or vertically (not diagonally). Count how many separate lit clusters exist in the grid.
`grid` is a 2D pixel grid of 0s and 1s, where 1 means a lit pixel. Two lit pixels belong to the same cluster if they are adjacent horizontally or vertically (not diagonally). Count how many separate lit clusters exist in the grid.
