Fix (#214) : added typing for consistent return type for add() method

[kisshan13]

Hey I have solved the issue #214 (Allow not to copy/paste throwOnTimeout) .

I added few types like :

export type Falsy = false;
export type Truthy = true;

export type BooleanTypeReturn<
	T extends Falsy | Truthy,
	TruthyReturn,
	FalsyReturn
> = T extends Truthy ? TruthyReturn : FalsyReturn;

I used these as generic types to achieve a consistent return type based on passed parameters .

So basically what this will do is :

import Queue from "p-queue"

const queue = new Queue({
  concurrency: 1,
  interval: 1500,
  intervalCap: 1,
  throwOnTimeout: true, 
})

// typed as number
const value1 = await queue.add(async () => 123)

// typed as number
const value2 = await queue.add(async () => 123, { throwOnTimeout: true })

You can review this and tell me any changes if required.

Thank you.