Function advent_of_code_2021::day_15::find_shortest_path

fn find_shortest_path(
    grid: &ExpandedGrid<'_>, 
    start: (usize, usize), 
    goal: (usize, usize)
) -> Option<usize>

Implement Dijkstra’s shortest path algorithm. Copied from BinaryHeap example and modified to get the edge costs from the provided grid. Originally accepted Grid but it was easier to use one type/method for both parts and the ExpandedGrid works the same as a Grid if it only has one tile on each axis.