fix: ensure onListen hooks are called when they should be

[bienzaaron]

This PR fixes an issue where the onListen application hooks don't run in some cases when they should:

1. When there is an onListen hook registered in a child encapsulation context, but the parent context does not have one
2. When there are multiple encapsulation contexts that are peers (i.e. at the same level / both children of the same parent), only the first will run

See example code:

const Fastify = require('./fastify.js')

const fastify = Fastify({ logger: true })

fastify.addHook('onListen', (done) => {
  console.log('i am called')
  done()
})

fastify.register((instance, opts, done) => {
  instance.addHook('onListen', (hookDone) => {
    console.log('i am also called')
    hookDone()
  })

  // create an encapsulation, and then create another immediately inside it
  instance.register((instance2, opts, done2) => {
    instance2.register((instance3, opts, done3) => {
      instance3.addHook('onListen', (hookDone) => {
        console.log('i am not called, because my parent does not have an onListen hook')
        hookDone()
      })
      done3()
    })
    done2()
  })
  done()
})

// since there is another context at this level (i.e. peer context), the hook inside this context won't run.
fastify.register((instance, opts, done) => {
  instance.addHook('onListen', (hookDone) => {
    console.log('i am not called because I am a peer context')
    hookDone()
  })
  done()
})

fastify.listen({ port: 3000 })

With the current version of fastify, this produces the following log output:

{"level":30,"time":1705470523577,"pid":99149,"hostname":"AJs-MacBook-Pro.local","msg":"Server listening at http://[::1]:3000"}
{"level":30,"time":1705470523578,"pid":99149,"hostname":"AJs-MacBook-Pro.local","msg":"Server listening at http://127.0.0.1:3000"}
i am called
i am also called

I believe the appropriate output would be:

{"level":30,"time":1705470550633,"pid":99225,"hostname":"AJs-MacBook-Pro.local","msg":"Server listening at http://[::1]:3000"}
{"level":30,"time":1705470550634,"pid":99225,"hostname":"AJs-MacBook-Pro.local","msg":"Server listening at http://127.0.0.1:3000"}
i am called
i am also called
i am not called, because my parent does not have an onListen hook
i am not called because I am a peer context

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

[climba03003]

Would it be easier to always share the same onListen array?
Then we don't need to lookup the children tree and search for the event listener.

this binding would fail, so it is not an option.

[metcoder95]

LGTM, nice catch 👍

The change should be ok, when creating the tree it seems we navigated it vertically but missed horizontally, that's the reason why the while does seem to do the trick

[mcollina]

lgtm