Post method is not able to properly download a Stream

Hi I'm not sure if this is an issue or I'm doing something wrong.
I'm trying to call an external API to download a PDF file that I will later encode into a base64 string.

I used .post from RESTDataSource class.
But the string I receive is not correct.

I tried the same using axios and everything is perfectly working.
This is the working code:

```
const response = await axios({
method: "post",
url: `${this.baseURL}/storefrontapi/hot/orders/${orderId}/export/pdf`,
headers: {
Accept: "application/json-patch+json, */*",
authorization: `Bearer ${this.context.token}`,
"Content-Type": "application/pdf",
},
responseType: "arraybuffer", // Ensure binary data is handled correctly
})
```

This is the not working call using RESTDataSource method.

```
const response = await this.post(`storefrontapi/hot/orders/${orderId}/export/pdf`, {
headers: {
Accept: "application/json-patch+json, */*",
authorization: `Bearer ${this.context.token}`,
"Content-Type": "application/pdf",
},
})
```

I can't use responseType here because is not supported, I didn't find any way to pass it to the post function.

Start by tracing the RESTDataSource.post entry point and its response handling for binary data; the issue provides no file or test path. The work is done when a POST can preserve the downloaded PDF bytes and support the needed response configuration, with a regression test covering the stream response.

Written by the indexing model from the issue text.