test: added tests for Decimal Isolate function

[HRIDYANSHU054]

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Describe your change:

• Add an algorithm?
  Added tests for Maths/DecimalIsolate function and extended comments about its usage

Before:

/*
 * function isolates the decimal part of a number.
 * Take the number and subtract it from the floored number.
 * Return the result.
 */

Now:

/*
 * This function isolates the decimal part of a number.
 * - If input is a number or a numeric string, it isolates and returns the decimal part.
 * - If input is an array:
 *    - It isolates the decimal part of the first element.
 *    - If the array contains more than one element, only the first element is considered.
 *    - If the array is empty, it returns 0.
 * - If input is not a number, a numeric string, or a valid first element array,
 *   the function returns 0.
 */

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new JavaScript files are placed inside an existing directory.
• All filenames should use the UpperCamelCase (PascalCase) style. There should be no spaces in filenames.
  Example:UserProfile.js is allowed but userprofile.js,Userprofile.js,user-Profile.js,userProfile.js are not
• All new algorithms have a URL in their comments that points to Wikipedia or another similar explanation.
• If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.81%. Comparing base (ff314a2) to head (053800f).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1752      +/-   ##
==========================================
+ Coverage   84.76%   84.81%   +0.05%     
==========================================
  Files         378      378              
  Lines       19742    19743       +1     
  Branches     2955     2956       +1     
==========================================
+ Hits        16735    16746      +11     
+ Misses       3007     2997      -10     

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