OptionalstreamFor a caller that has already given stdout to something else — the CLI's --out -, which
streams a workbook down the pipe — a report written to stdout would interleave two payloads
on one stream and corrupt both. Such a caller passes stderr instead.
Styling follows whichever stream is actually written to, so a report redirected to a terminal's stderr still gets its colors and one redirected into a file still does not.
Where the report goes. Defaults to stdout.