LoadingTimeout is missing cleanup function

Hi @cyntler ,

we are using v1.7.0 to preview Images selected in an Input.

While developing we experienced the following Console Warning:

`console.js:273 Warning: Can't perform a React state update on an unmounted component. This is a no-op, but it indicates a memory leak in your application. To fix, cancel all subscriptions and asynchronous tasks in a useEffect cleanup function.
in LoadingTimeout (created by Contents)
in Contents (created by ProxyRenderer)`

So we dug a bit into the readme, tried to set the `showLoadingTimeout` to false, yet, the warning continued to show up.

Like the warning suggested, we then worked on a cleanup function. Which would change the useEffect of the `LoadingTimeout` component to look like this:

```
useEffect(() => {
if (shouldLoadingRender) {
return () => {};
}

const timer = setTimeout(
() => {
setShouldLoadingRender(true);
},
typeof config?.loadingRenderer?.showLoadingTimeout === "number"
? config.loadingRenderer.showLoadingTimeout
: 500,
);

return () => {
clearTimeout(timer);
}
}, [config?.loadingRenderer?.showLoadingTimeout]);
```

Notice the early exit if `showLoadingTimeout` is false.
We think this might be relevant for every version, so i createe this issue.

Let us know, what you think.

Regards,
Jakob