feat: add support for eta@3.x

[multivoltage]

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

Goal

I want etajs@3.x support for this project. Hope my PR or other people want same feature

What I did not

Not edited documentation since probably I cannot say to be skilled enough in this project

What I did

I tried to make all the tests work by changing as few things as possible. Unfortunately, one big change involves creating an Eta instance with new Eta().
I had to change many parts of the tests. Not sure about many changes. Finally I started a test project by installing fastify, and linking index.js. I managed to get the basic example working:

import view from '../point-of-view-new'
import { Eta } from 'eta'

const eta = new Eta()

const fastify = Fastify({
    logger: true
  })
  
fastify.register(view, {
    engine: {
      eta
    },
});

  
// Declare a route
fastify.get('/', function (request, reply) {
    reply.view("/templates/hello.eta", { name: "diego" });
})

[mcollina]

lgtm

[multivoltage]

@mcollina
maybe I should have created a special issue for this change?

[mcollina]

why?

[multivoltage]

Honestly I don't know. Is my second time I submit a pr ;)

[aalfiann]

I have issue, this PR doesn't work if eta using includeFile.

[Eomm]

Please open a new detailed issue adding a Minimal, Reproducible Example.