Pool initialization rejections cannot be handled currently, and they return errors in the global main handler of javascript.

There's no way to handle pool init errors. Consider a scenario where a website's CSP doesn't allow us to run a worker; the pool init will fail to make a handshake with the worker because the worker never gets initialized. If we queue tasks to the pool, then the PromiseLike returned from the `queue` method of the `pool` class is not catchable.

For example, if you have this code:

```ts
let work;
try {
work = new Worker(new URL(`data:text/javascript;base64:${workerJs}`))
} catch (e) {
work = new Worker();
}
const pool = Pool(() =>
spawn(work, {
timeout: 1000,
}),
1
);

const allTasks = [];
for (let i = 0; i < 10; i ++) {
const p = new Promise(async (resolve, reject) => {
try {
const t = await pool.queue((e) => {});
return resolve(t);
} catch (e) {
return reject(e);
}
});
allTasks.push(p.catch(e => {console.log(e)}));
}

// You can never catch it since it always throws errors in the main thread.
await Promise.all(allTasks);
```

## Possible Fix

When a pool fails to init, it inserts an error event to the `eventSubjects` stream:
https://sourcegraph.com/github.com/andywer/threads.js/-/blob/src/master/pool.ts?L151&subtree=true

```
this.eventSubject.error(error)
```

We can't catch the error because the `taskCompletion` method does not subscribe to the error events. It's only subscribing to the `next()` events. Adding a case for the error in the below code appropriately rejects the error.
https://sourcegraph.com/github.com/andywer/threads.js/-/blob/src/master/pool.ts?L233&subtree=true#tab=references

```
// minified.
taskCompletion(e) {
return new Promise((t, r) => {
const n = this.events().subscribe({
next(o) {
o.type === u.PoolEventType.taskCompleted && o.taskID === e
? (n.unsubscribe(), t(o.returnValue))
: o.type === u.PoolEventType.taskFailed && o.taskID === e
? (n.unsubscribe(), r(o.error))
: o.type === u.PoolEventType.terminated &&
(n.unsubscribe(),
r(Error("Pool has been terminated before task was run.")));
},
error: r
});
});
```

I can create a PR with the fix but want to know if I am doing something wrong.