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:

• [x] I have read CONTRIBUTING.md.
• [x] This pull request is all my own work -- I have not plagiarized.
• [x] I know that pull requests will not be merged if they fail the automated tests.
• [x] This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• [x] All new JavaScript files are placed inside an existing directory.
• [x] 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
• [x] All new algorithms have a URL in their comments that points to Wikipedia or another similar explanation.
• [x] If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.