Add :Cycle detection in undirected graph using Union–Find

[Amritray01]

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Description of Change

Added a new implementation graph/cycle_check_undirected_dsu.cpp for Cycle Detection in Undirected Graph using Disjoint Set Union (Union–Find) with path compression and union by rank.
This complements the existing directed graph version and efficiently detects cycles in O(E α(V)) time.
The program includes inline tests, handles self-loops and disconnected graphs, and follows C++17 and Doxygen documentation standards.

Checklist

• Added description of change
• File name matches [File name guidelines](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/CONTRIBUTING.md#New-File-Name-guidelines)
• Added example tests that pass successfully
• Added Doxygen-style documentation and comments
• PR title follows semantic [commit guidelines](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/CONTRIBUTING.md#Commit-Guidelines)
• Verified no duplicate implementation exists
• I acknowledge all contributions are made under the project’s license

Notes:
Efficient DSU-based cycle detection for undirected graphs — complements cycle_check_directed_graph.cpp.
Expected output during self-test:

Test 1 (triangle): Cycle
Test 2 (chain): No cycle
Test 3 (disconnected): Cycle
Test 4 (self-loop): Cycle

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