Improve `_create_void_ptr_wrapper()`

> The thinking is to use something similar to `modify_func()` below inside `_create_void_ptr_wrapper()`. My hope is that since the intrinsic `impl` is just a wrapper returning the same `codegen` function, we can create a dummy wrapper and modify its `__code__` attributes dynamically.

_Originally posted by @leofang in https://github.com/NVIDIA/cccl/pull/4249#discussion_r2066895904_