* changes made to the following files:
- mod.js
- gcd.js
* updated BigNumber implementation and added validating tests
* added validating test cases
* updated test cases
* formatted code
* Made updates according to requirement
used mathjs floor in mod.js
imported mod in gcd.js
made mod work for negative divisors
wrote and updated tests to validate new behavior
* updated mod in arithmetic.js
* added tests for modNumber function
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Co-authored-by: Jos de Jong <wjosdejong@gmail.com>