I just added serendipity_event_schema to Spartacus. It is a plugin that adds schema.org markup to your blog. Two kinds of schema: One, it automatically marks blog entries as such, and you can set author information in the settings it will then use. Second, if you create some fields for that via the entryproperties plugin, it will then create the correct markup for reviews. The included documentation (linked in the settings) explains how.
This plugin has been in use in my blog for some years now. It was available via a custom github repo at https://github.com/onli/serendipity_event_schema (which I will now archive). Google really does pick up the review markup, so potentially other search engines as well. Give it a try :)