What does this PR do?

Fixes worker tests but it makes these changes to WebWorker.

was reimplemented a little on aug 11:

• A worker's event loop impacts the main process' event loop. Meaning if you setTimeout in a worker/listen for messages, it keeps main alive.
• Worker is by default .ref(), but workers will exit if their event loop dies.
• If you do addEventListener("message") on a message port or the global, this refs the event loop.
• If you do worker.unref() this no longer makes the worker's event loop affect the caller's. This is what esbuild depends on.
• We were not freeing WebWorker struct. This was because its a little complex. I solved it by assigning vm to null when the vm is done with, then the while(true) loop for the worker (the source of the UAF) would call real deinit. It's not really that complex with the changes to the worker event loop. .terminate sets a flag to tell the worker to exit the event loop, and the deinit is called from within spin() on the Worker's thread.

I'd like a close review to make sure i did everything right. I triple checked my uses of event loop refs and memory usage in the worker zig file.

• Documentation or TypeScript types (it's okay to leave the rest blank in this case)
• Code changes

How did you verify your code works?

I ran unit tests. For testing large scale worker event loop stuff.

import { Worker, isMainThread, workerData } from "worker_threads";

if (isMainThread) {
  for (let i = 0; i < 1000; i++) {
    const w = new Worker("/Users/dave/code/bun/test/js/web/worker-demo.mjs", { ref: false, workerData: i });
    let recieved = false;
    w.on("message", msg => {
      if (msg === "initial message") {
        recieved = true;
      } else {
        console.log("WHAT?", msg);
      }
    });
    setTimeout(() => {
      if (!recieved) {
        w.terminate();
        console.log("worker", i, "did not respond");
      }
    }, 5000 + 500);
  }
} else {
  setTimeout(() => {
    self.postMessage("initial message");
    console.log("workerid=", workerData);
  }, Math.random() * 5000 + 500);
}

Pipe this to a file to see that exactly 1000 lines are output.