Port harvester for the BfS' website from Python to Rust.

I opted to drop the extra scraping of the multimedia section since it missed the subsections and thereby a lot of entries but more importantly all media entries have a text-form article which is found via the usual search and is much more helpful than the video or audio alone yet still includes a link.

Also enables the resultsPerPage parameter for other GSB-based scrapers which means their serp-* cached responses need to be deleted before this is deployed.