Add additional edge cases to GCD unit tests

[Saniya2701]

• Added tests for equal numbers, prime numbers, single-element arrays, and large numbers
• Improved coverage for GCD algorithm

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.89%. Comparing base (2911a7b) to head (f321567).

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #7174   +/-   ##
=========================================
  Coverage     78.89%   78.89%           
- Complexity     6857     6858    +1     
=========================================
  Files           771      771           
  Lines         22686    22686           
  Branches       4456     4456           
=========================================
+ Hits          17898    17899    +1     
  Misses         4072     4072           
+ Partials        716      715    -1     

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