Clarify setTimeout return value in timers documentation (Node.js returns a Timeout object, not just an ID)

[ShubhamOulkar]

Doc URL(s)

https://nodejs.org/en/learn/asynchronous-work/discover-javascript-timers

Description of the problem

In Node.js, setTimeout() and setInterval() returns a Timeout object, which can be used to cancel or manipulate the timer. In browsers, it returns a numeric timer ID. The current Node.js documentation says these functions return a "timer ID", which can be misleading in the Node context.

Docs should reflect Node-specific behavior more precisely

1. Browser devs might expect a number and be confused when console.log(setTimeout(...)) gives them an object.
2. They might not realize unref() and other methods are available.

[avivkeller]

Feel free to open a PR 😃