Working around ERR_PACKAGE_PATH_NOT_EXPORTED

I'm trying to print your default thread size for a dry run purpose (without initialising a pool first).

```js
let {
dryRun,
threads = require('threads/dist/master/implementation').defaultPoolSize,
// ...
} = argv;

if (dryRun) {
console.log('threads', threads);
}
```

I'm having trouble updating to the latest version because of ERR_PACKAGE_PATH_NOT_EXPORTED. My workaround is:

```js
let {
dryRun,
threads,
// ...
} = argv;

let pool = Pool(() => spawn(new Worker('foo')), ...[threads].filter(Boolean));

if (dryRun) {
console.log('threads', pool.workers.length);
}
```

It works, but the original was more elegant. I know your implementation is simple and based on `cpus().length`, but I'd prefer not diverge from your default and start guessing wrong. What are your thoughts? Should a default config be exposed? If my workaround is what you recommend, feel free to close this issue. Thanks.