Change the position of sink in the file to position. The argument sink must be either a
sink produced by this file handle, or a BufferedSink that directly wraps such a sink. If the
parameter is a BufferedSink, it emits for buffered bytes.
Change the position of source in the file to position. The argument source must be either
a source produced by this file handle, or a BufferedSource that directly wraps such a source.
If the parameter is a BufferedSource, it will skip or clear buffered bytes.