emoji_eventsShortest delivery route (Dijkstra)

A delivery company stores its road network as a dict: graph[a][b] = minutes (one-way roads). Write shortest_route(graph, start, goal) that returns (total_minutes, [start, ..., goal]) for the fastest route.

• Return (None, []) when the goal can't be reached.
• start == goal returns (0, [start]).
• Nodes that only appear as destinations are valid nodes.
• It must be fast: the last test has 2,000 nodes. Use a priority queue (heapq).

Acceptance criteria

• Ties may return any one of the fastest routes; the tests only check routes that are unique.
• The tests at the bottom print All tests passed.