Factorial for Big Numbers

[craftycoder07]

• [x] I have performed a self-review of my code
• [x] My code follows the style guidelines of this project
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes
• [x] Comments in areas I changed are up to date
• [x] I have added comments to hard-to-understand areas of my code
• [ ] I have made corresponding changes to the README.md

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (41bbea3) 95.75% compared to head (e76f4f2) 95.76%.

:exclamation: Current head e76f4f2 differs from pull request most recent head f0db669. Consider uploading reports for the commit f0db669 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #387 +/- ## ======================================= Coverage 95.75% 95.76% ======================================= Files 218 218 Lines 8887 8901 +14 ======================================= + Hits 8510 8524 +14 Misses 377 377 ``` | [Impacted Files](https://codecov.io/gh/TheAlgorithms/C-Sharp/pull/387?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None) | Coverage Δ | | |---|---|---| | [Algorithms/Numeric/Factorial.cs](https://codecov.io/gh/TheAlgorithms/C-Sharp/pull/387?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-QWxnb3JpdGhtcy9OdW1lcmljL0ZhY3RvcmlhbC5jcw==) | `100.00% <100.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None)

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