Add kruskal algorithm

[Raghu0703]

Description

This PR adds an implementation of Kruskal's Algorithm for finding the Minimum Spanning Tree (MST) in weighted undirected graphs. This addresses the feature request in issue #7067.

Kruskal's algorithm is a fundamental graph algorithm that builds the MST by sorting edges by weight and adding them one by one, using a Union-Find data structure to avoid creating cycles.

Changes Made

• ✅ Added Kruskal.java - Complete implementation with Union-Find optimization
• ✅ Added KruskalTest.java - Comprehensive test suite with 9 test cases covering various scenarios
• ✅ Documentation - Included detailed JavaDoc comments explaining the algorithm
• ✅ Optimizations - Implemented path compression and union by rank for efficiency

Algorithm Details

• Time Complexity: O(E log E) where E is the number of edges
• Space Complexity: O(V + E) where V is the number of vertices
• Key Features:
  • Uses Disjoint Set (Union-Find) for efficient cycle detection
  • Sorts edges by weight using Java's built-in sorting
  • Handles edge cases like disconnected graphs and empty inputs

Testing

All tests pass successfully and cover:

• ✅ Simple connected graphs
• ✅ Disconnected components
• ✅ Complete graphs
• ✅ Graphs with equal-weight edges
• ✅ Edge cases (empty graphs, single edges)
• ✅ Input validation (null checks, invalid vertex counts)

References

• Kruskal's Algorithm - Wikipedia
• Union-Find Data Structure

Fixes #7067

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Checklist

• [x] I have read CONTRIBUTING.md
• [x] This pull request is all my own work -- I have not plagiarized it
• [x] All filenames are in PascalCase
• [x] All functions and variable names follow Java naming conventions
• [x] All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations
• [x] All new code is formatted with mvn spotless:apply