R and lobstr disagree on size of bytecode

For example:

```R
bytecode <- .Internal(bodyCode(mean))
object.size(bytecode)
lobstr::obj_size(bytecode)
```

I see:

```R
> bytecode <- .Internal(bodyCode(mean))
> object.size(bytecode)
848 bytes
> lobstr::obj_size(bytecode)
792 B
```

