Add Kruskal's Algorithm implementation

[RamsaiPolisetti]

Summary

This PR adds an implementation of Kruskal's Minimum Spanning Tree (MST) algorithm to the graph package.
Kruskal’s algorithm is a classic greedy algorithm that finds the MST of a connected, undirected, weighted graph by selecting edges in increasing order of weight while avoiding cycles.

Implementation Details

• Added KruskalsAlgorithm.java under src/main/java/com/thealgorithms/graph/
• Includes:
  • Edge class for representing edges
  • DSU (Disjoint Set Union / Union–Find) for cycle detection
  • kruskalMST() method implementing the core algorithm
• Clean, modular, and follows project style conventions.

Tests

• Added a corresponding JUnit test under
  src/test/java/com/thealgorithms/graph/
• Tests verify:
  • The MST has exactly V - 1 edges.
  • The smallest edges are correctly selected.
  • The algorithm avoids cycles.

All tests pass using ./gradlew test.

Checklist

• [x] Added implementation
• [x] Added tests
• [x] Code compiles successfully
• [x] Tests pass
• [x] Follows coding style and package structure

[codecov-commenter]

Codecov Report

:x: Patch coverage is 0% with 59 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 78.29%. Comparing base (2c4bf3c) to head (8bbb886). :warning: Report is 11 commits behind head on master.

Files with missing lines	Patch %	Lines
...ava/com/thealgorithms/graph/KruskalsAlgorithm.java	0.00%	59 Missing :warning:

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #7121      +/-   ##
============================================
- Coverage     78.51%   78.29%   -0.23%     
+ Complexity     6752     6751       -1     
============================================
  Files           759      760       +1     
  Lines         22402    22461      +59     
  Branches       4400     4410      +10     
============================================
- Hits          17589    17585       -4     
- Misses         4108     4169      +61     
- Partials        705      707       +2     

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