Geocoding error on fresh Wordpress Install
It sounds like an incomplete install. You might need to run composer install from inside the ext/org.wikimedia.geocode folder.
But you don't need the extension if you just want to use basic geocoding in civicrm, you just need to set it up at administer - system settings - mapping and geocoding. The extension just adds more features.
UPDATE: It seems like the download version of the extension was an incomplete install. A new version is now available.