Use csv_string() to streamline CSV generation

[cclauss]

Related to #6621 and #6653 which also use csv_string().

The csv_string() function uses iteration to generate the contents of a comma-separated values file as one long string.
For large datasets, this approach should use far less memory than storing all intermediate results as lists of lists of values.

Technical

Testing

Screenshot

Stakeholders

[jimchamp]

Thanks @cclauss, this lgtm!
We'll probably want to use csv_string() in the functions which generate reading log and list overview csvs --- this is something that I'll do later.