Added a feature of Disabling the Start button after one Click in JS file

[Aadarsh-Mourya]

In this updated code, the "start" button is disabled when clicked, and it is re-enabled only when the "reset" button is clicked. The "reset" button is disabled when clicked and re-enabled only when the "start" button is clicked. This ensures that the "start" button can be clicked only once until the "reset" button is clicked.