Cut the dijkstra_algorithm.py time in half with various tricks

[Mortal]

Implement a number of performance optimizations that altogether cut down the running time to about half, as tested with a 2905 * 4029 raster with 1 start point and 1 end point.

• Don't use queue.PriorityQueue, as it is a threadsafe queue with unnecessary locking - use heapq.heappush() and heappop() instead.

• Don't use function calls - instead, inline all functions. Almost all the functions in the old code were only used in one place.

• Instead of dicts and sets, use lists of lists, which have faster lookup.

• Reduce the number of calls to feedback.setProgress().

[Gooong]

Hi @Mortal, thanks for the improvement. Will review and test this PR and release soon!