test: add tests for Eucledian GCD Algorithm

[malpotra]

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[appgurueu]

We already have Maths/GetEuclidGCD.js (iterative). The iterative version is strictly better than the recursive one (doesn't waste stack space; JS can not be trusted to do tail call optimization).

So, the iterative version in Recursive/EucledianGCD.js should be removed. I'm not sure whether the recursive version should be kept.

Either way, the tests for the GCD should not be duplicated. These functions (Maths/GetEuclidGCD.js & recursive GCD) solve the same problem - and with the same time complexity even - and thus should use the same tests.

[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).