Add Kruskal's MST algorithm

[ArpitaHanjagi]

Kruskal’s Algorithm is a greedy algorithm used to find the Minimum Spanning Tree (MST) of a connected, weighted graph. It works by:

Sorting all edges in increasing order of weight.

Picking the smallest edge that doesn’t form a cycle with edges already chosen.

Repeating step 2 until all vertices are connected.

It ensures a spanning tree with minimum total weight.

[Copilot]

Pull Request Overview

This PR adds an implementation of Kruskal's Minimum Spanning Tree (MST) algorithm to the graph algorithms collection. The implementation uses a Union-Find (Disjoint Set Union) data structure to efficiently detect cycles while constructing the MST by iteratively selecting the smallest edges that don't form cycles.

Key changes:

• Implementation of Kruskal's algorithm with Union-Find optimization (path compression and union by rank)
• Helper functions for disjoint set operations (make_set, find_set, union_sets)
• Example usage demonstrating the algorithm on a 4-vertex weighted graph