I blindly assumed the original implementation also did this, but this
version `std::variant<Ts...>` objects from being reinitialized if we're
deserializing a variant that's also currently active in the object we're
deserializing into. For simple structs this won't make any difference,
but in yabridge we often use variants to differentiate between things
like single precision and double precision audio buffers. Those buffers
are allocated on the heap, so recreating the objects every time we
deserialize them adds a lot of unnecessary overhead.