Add calculator.js file with basic calculator functions

[chitra-dongare]

Created a new file calculator.js that includes basic calculator functions such as sum, difference, product, and division.
This addition provides a simple utility to perform arithmetic operations and can be used for learning or integration in other parts of the project.

[vercel]

@chitra-dongare is attempting to deploy a commit to the sadanandpai's projects Team on Vercel.

A member of the Team first needs to authorize it.

[sadanandpai]

We already've calculator added. If an improvement is needed update it.

https://jscodechallenges.vercel.app/challenges/functions#1-design-a-calculator-interface-for-2-number-inputs-which-can-perform-sum-difference-product-and-dividend-whenever-invoked-on-the-same-interface