test: add tests for Eucledian GCD Algorithm

[malpotra]

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Describe your change:

• [ ] Add an algorithm?
• [ ] Fix a bug or typo in an existing algorithm?
• [ ] Documentation change?

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• [ ] I have read CONTRIBUTING.md.
• [ ] This pull request is all my own work -- I have not plagiarized.
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• [ ] If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.

[appgurueu]

As said, I think the existing GCD tests should be reused (or the recursive function should be removed altogether, as it is strictly inferior).