request new function to get the childtable

For example, Delivery Note and Delivery Note Item have a parent-child relationship.

I expect a function that can query the fields of the parent table Delivery Note and the child table Delivery Note Item at once.

I tried reading using something like the following, but I couldn't read the ChildDocType.

After carefully studying Frappe's logic for reading child table data, it should be similar to the following reading logic, note the parameter **parent=Delivery%20Note**

```
http://192.168.32.2:8001/api/resource/Delivery%20Item?&parent=Delivery%20Note&fields=[%20"name",%20"item_code",%20"qty"%20]&filters=[[%20"parent",%20"=",%20"MAT-DN-2024-00001%20"]]
```

```
*/
export const useFrappeCascadeGetDocList = >(MainDocType: string, ChildDocType: string, mainArgs?: GetDocListArgs, childArgs?: GetDocListArgs, swrKey?: Key, options?: SWRConfiguration) => {

const { url, db } = useContext(FrappeContext) as FrappeConfig;

const swrResult = useSWR(
swrKey === undefined ? `${getRequestURL(MainDocType, url)}?${getDocListQueryString(mainArgs)}` : swrKey,
() => db.getDocList(MainDocType, mainArgs),
options
);

const childSWRKey = swrResult.data ? `${getRequestURL(ChildDocType, url)}?${getDocListQueryString(childArgs)}` : null;

const childSWRResult = useSWR(childSWRKey, () => db.getDocList(ChildDocType, childArgs), {
...options,
revalidateOnFocus: false,
shouldRetryOnError: false,
});

return {
mainDocs: swrResult,
childDocs: childSWRResult,
};
};
```

Start with the existing db.getDocList entry point and the proposed useFrappeCascadeGetDocList hook, then inspect getRequestURL and getDocListQueryString to understand how parent and child queries are built. Define the expected parent-child result shape and query behavior, then add coverage for retrieving Delivery Note and Delivery Note Item data together.

Written by the indexing model from the issue text.