Added debounce and throttle utility functions for Modern Development

[BEASTSHRIRAM]

PR Description:

this is my first pr in this repo and the implementations are debounce and throttle, These utilities provide three debounce implementations and four throttle implementations with practical examples for optimizing ServiceNow client-side performance.

Pull Request Checklist

Overview

• Put an x inside of the square brackets to check each item.
• [x ] I have read and understood the CONTRIBUTING.md guidelines
• [ x] My pull request has a descriptive title that accurately reflects the changes and the description has been filled in above.
• [x ] I've included only files relevant to the changes described in the PR title and description
• [x ] I've created a new branch in my forked repository for this contribution

Code Quality

• [x ] My code is relevant to ServiceNow developers
• [x ] My code snippets expand meaningfully on official ServiceNow documentation (if applicable)
• [x ] I've disclosed use of ES2021 features (if applicable)
• [ x] I've tested my code snippets in a ServiceNow environment (where possible)

Repository Structure Compliance

• [ x] I've placed my code snippet(s) in one of the required top-level categories:
  • Core ServiceNow APIs/
  • Server-Side Components/
  • Client-Side Components/
  • Modern Development/
  • Integration/
  • Specialized Areas/
• [x ] I've used appropriate sub-categories within the top-level categories
• [ x] Each code snippet has its own folder with a descriptive name

Documentation

• [x ] I've included a README.md file for each code snippet
• [x ] The README.md includes:
  • Description of the code snippet functionality
  • Usage instructions or examples
  • Any prerequisites or dependencies
  • (Optional) Screenshots or diagrams if helpful

Restrictions

• [x ] My PR does not include XML exports of ServiceNow records
• [x ] My PR does not contain sensitive information (passwords, API keys, tokens)
• [ x] My PR does not include changes that fall outside the described scope

[github-actions]

Thank you for your contribution. However, it doesn't comply with our contributing guidelines.

As a reminder, the general requirements (as outlined in the CONTRIBUTING.md file) are the following: follow the folder+subfolder guidelines and include a README.md file explaining what the code snippet does.

Validation errors:

Folder structure violations found:
 - Move 'Modern Development/Debounce and Throttle/README.md' under a valid folder hierarchy (Category/Subcategory/Use-Case/your-file). Files directly inside 'Modern Development' or its subcategories are not allowed.
 - Move 'Modern Development/Debounce and Throttle/combined-usage.js' under a valid folder hierarchy (Category/Subcategory/Use-Case/your-file). Files directly inside 'Modern Development' or its subcategories are not allowed.
 - Move 'Modern Development/Debounce and Throttle/debounce.js' under a valid folder hierarchy (Category/Subcategory/Use-Case/your-file). Files directly inside 'Modern Development' or its subcategories are not allowed.
 - Move 'Modern Development/Debounce and Throttle/throttle.js' under a valid folder hierarchy (Category/Subcategory/Use-Case/your-file). Files directly inside 'Modern Development' or its subcategories are not allowed.

Review your contribution against the guidelines and make the necessary adjustments. Closing this for now. Once you make additional changes, feel free to re-open this Pull Request or create a new one.