feat: add support for iterators

[metcoder95]

This is a first iteration of the support for (async)iterators on Piscina.

It is quite raw as I wanted to experiment first a bit how it can look like and also possibly draft the API of it; I'm still having some doubts about how can it look like and what differentiation can it have, so I just came with a easy one of, returning an Stream every time an iterator is identified while handling the worker's workload.

Further optimizations:

• Replace port.postMessage with a ring buffer to reduce overhead - for further PRs
• Properly implement WorkerStream which will be an abstraction of the ring buffer implementation - same as previous point
• Shape API
• Docs

[metcoder95]

It should be ready for review; I'm quite curious about seeing an ergonomic enough API. I already have some baseline for optimizations, especially around messages between worker and main thread, but I'd like to start gathering feedback about the API shape and leave the further enhancements for upcoming PRs

[metcoder95]

I'll be adding docs later this week