Function onCreateCustomModelLoader

onCreateCustomModelLoader(
callback: CustomLoaderCallback,
opts?: CustomLoaderOptions,
): () => void
Register a custom loader callback. For every file that is requested this callback is called with the url and mimetype. It should return a custom loader or null if it does not want to handle the file.
Parameters
- callback: CustomLoaderCallback
  The callback to register
- Optionalopts: CustomLoaderOptions
  Optional options for the loader (e.g. name, priority)
Returns () => void
A function to unregister the callback
Example
```
import { onCreateModelLoader } from "@needle-tools/engine";
const unregister = onCreateModelLoader((url, mimetype) => {
    if (mimetype === "application/vnd.usdz+zip") {
        return new CustomLoader();
    }
    return null;
```