so cacheTime was really confusing because it seemed like "this is the amount time we cache data for", but that's not what it is. So a rename had to happen. We had some discussion on the public roadmap (https://github.com/TanStack/query/discussions/4252) about what it's gonna be. I'm usually against abbreviations, simply because there's always someone who doesn't understand what it means. But all other suggestions like inactiveCacheTime also had room for interpretation. gc is an abbreviation that is known well enough (think git gc), and it's also not an option that you will customize on a daily basis (usually once, globally).
