if it helps: it's pretty typical to attach the allocator to the object directly, so you dont have to pass it everywhere. for library consumers, just build a global allocator and use that. io will just "have to be passed the annoying way" in libraries (but a consumer can also also easily globalize that).
I'm assuming you're talking about the "managed" pattern you'd see in stuff like Hashmaps and ArrayLists. To my knowledge that style is falling out of favor, and I think the managed versions will be removed from the standard library.
I haven't seen anyone use a global allocator in the way you're talking about, and if you did I feel like it goes directly against the Zig ethos. Part of the benefit of allocators being passed around is that all allocation are explicit.
