feat: Add Dijkstra's Algorithm with priority queue

[joaovicenteft]

Adds Dijkstra's algorithm using a min-heap priority queue as requested in #1537.

• Graph: Adjacency list with weights.
• PQ: Binary heap with insert/decrease simulation.
• Example: 5-node graph, outputs shortest distances from node 0.

Tested with GCC; no memory leaks.

Fixes #1537.

[github-actions]

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