feat: Added Double Factorial Iterative Implementation

[SpiderMath]

This pull request aims to add the iterative implementation of double factorial in TypeScript
Here's the entry I aim to add an implementation to: https://the-algorithms.com/algorithm/double-factorial-iterative

[appgurueu]

Code-wise fine, but unfortunately not really algorithmically interesting...

[SpiderMath]

Code-wise fine, but unfortunately not really algorithmically interesting...

Yeah, that is indeed true. This code does not really have anything particularly interesting going for it. The sole reason I added this is so that the TypeScript implementations are available for more algorithms and it was the first one which I saw which didn't have an implementation.
However, I don't mind if you reject this PR since the code is pretty trivial and boring, and isn't that much of a valuable addition to the repository

[SpiderMath]

Could you please atleast leave a reply @appgurueu ...?

[SpiderMath]

Umm, a response or a reply would be highly appreciated

[appgurueu]

Sorry for the late reply. I am pretty indecisive on this, which unfortunately lead to me postponing & forgetting about it. Well, nothing has changed; I still think this is relatively straightforward, about as interesting as the factorial implementation - it may be warranted on these grounds, also considering that it has some applications in combinatorics. I'm fairly neutral on this; I'm not opposed to merging this. @raklaptudirm thoughts?

[raklaptudirm]

The implementation seems to be of good quality, so I approve of its merge.

[appgurueu]

I had to resolve a merge conflict, so you'll have to reapprove @raklaptudirm

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.00%. Comparing base (26ac72d) to head (ecc6a9b).

❗ Current head ecc6a9b differs from pull request most recent head 4c87609. Consider uploading reports for the commit 4c87609 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #187      +/-   ##
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+ Coverage   96.98%   97.00%   +0.01%     
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  Files          97       98       +1     
  Lines        1793     1800       +7     
  Branches      345      346       +1     
==========================================
+ Hits         1739     1746       +7     
  Misses         54       54              

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