Support partial download for the bucket::download_to_stream. This is permitted in the GridFS specification under Partial File Retrieval:

In the case of download_to_stream, drivers are not required to support partial file retrieval. If they choose to do so, drivers can support this operation by adding ‘start’ and ‘end’ to their supported options for download_to_stream. These values represent non-negative byte offsets from the beginning of the file. When ‘start’ and ‘end’ are specified, drivers return the bytes of the file in [start, end). If ‘start’ and ‘end’ are equal no data is returned.