nitpick: would it be better to default to . if download_path is not provided by the user?

So we are zipping all the files we are intended to download into a zip and then unzip it at the end? I'm curious why are we doing this, like what is the benefit of this solution vs downloading each individual file separatly and put them into a dedicated directory?

The QDR provides zip files for the GET:study_id and POST:bulk file_ids. We can also get single files via a GET request that is not a zip file. I can add a flag for downloading file_ids in bulk (zip) or one at a time (not zipped).

For the latter, should we rename the file after download? For example, if we download file_id=45139 should we rename the downloaded file from ‘45139’ to ‘Baum-et-al_INTERVIEW_GUIDE.pdf’? Or just log the filename at download?

I think we should not use the bulk endpoint for downloading using file IDs, I remember they said there are some size limitations on that endpoint. Even though we are very unlikely to hit by that limitation with the current HEAL studies they have on QDR, I think it is still better user experience to download them one by one by using their file IDs. So we don't really need to worry about the bulk file download endpoint for now
But we should definitely rename each individual files using their original filenames

Refactored to download single files from the GET:datafile/{id} endpoint. The data get written into the filename that is listed in the Content-Disposition response header.