perf(index): use spread over Object.assign()

[Fdawgs]

Nearly twice as fast, see https://github.com/RafaelGSS/nodejs-bench-operations/blob/main/RESULTS-v18.md#objectassign-vs-spread-operator

Checklist

• run npm run test and npm run benchmark
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[Eomm]

Are not we in the small object case?

[Uzlopak]

Actually, it is not noticable for most cases. If you use a delegator, then you should notice.

[Fdawgs]

Are not we in the small object case?

Original code was creating a new object, so according to that table it was ~9m vs ~16m

[Fdawgs]

Actually, it is not noticable for most cases. If you use a delegator, then you should notice.

Learnt something new today, thanks @Uzlopak!

Not worth looking at in other repos then?

[Uzlopak]

I wouldnt say that. Here in fastify-cors if you dont use that delegator style, than you will call that object merging only once. If you use delegator than it should be merging the object on every request.

But there are potentially other repos where object merging happens on every request and not only on startup, where it is worth to investigate it further.