Implementing BFS for unweighted graphs

[aparibocci]

This PR aims to implement breadth-first search for unweighted graphs, starting at the given node.

The algorithm has a time complexity of O(|V| + |E|), where:

• |V| is the number of nodes in the graph;
• |E| is the number of edges in the graph.

[aparibocci]

Hello @StepfenShawn, could I ask you to have a look at this MR when you have the opportunity?

Thank you in advance!