text: Title: `None` RawKernel argument is turned into 0xffffffff instead of NULL pointer
  Body: ### Description
  
  I spent this evening chasing a memory corruption bug. As it turns out, the cause was that a `None` argument passed to a `cupy.RawKernel` turned into a pointer with the address `0xffffffff` (i.e. `-1`). I would have expected the address `0`, or at least an address equal to `NULL` or maybe `nullptr`, but `0xffffffff` caught me by surprise. What is going on there?
  
  I found that I can pass `0` from Python to get a `NULL` pointer in the kernel, but it feels a bit dirty, because `0` is of type `int`, but the usual arguments is of type `cupy.ndarray`. Is it okay to just pass `0` when one wants `NULL`, or is there a "more proper" way to obtain a `NULL` value in Python?
  
  ### To Reproduce
  
  ```python
  import cupy
  
  # This prints
  #0xffffffff (nil)
  #0xffffffff (nil)
  source = r"""
  extern "C" __global__
  void kernel(const float *ptr){
      printf("%p %p\n", ptr, NULL);
  }
  """
  
  grid_dim = (1,)
  block_dim = (2,)
  args = (None,)
  
  cupy.RawKernel(source, "kernel")(grid_dim, block_dim, args)
  ```
  
  ### Installation
  
  Wheel (`pip install cupy-***`)
  
  ### Environment
  
  ```
  OS                           : Linux-6.8.0-55-generic-x86_64-with-glibc2.39
  Python Version               : 3.12.4
  CuPy Version                 : 13.3.0
  CuPy Platform                : NVIDIA CUDA
  NumPy Version                : 1.26.3
  SciPy Version                : 1.14.1
  Cython Build Version         : 0.29.36
  Cython Runtime Version       : None
  CUDA Root                    : /usr/local/cuda
  nvcc PATH                    : /usr/local/cuda/bin/nvcc
  CUDA Build Version           : 12060
  CUDA Driver Version          : 12060
  CUDA Runtime Version         : 12060 (linked to CuPy) / 12060 (locally installed)
  CUDA Extra Include Dirs      : []
  cuBLAS Version               : 120604
  cuFFT Version                : 11300
  cuRAND Version               : 10307
  cuSOLVER Version             : (11, 7, 1)
  cuSPARSE Version             : 12504
  NVRTC Version                : (12, 6)
  Thrust Version               : 200600
  CUB Build Version            : 200600
  Jitify Build Version         : <unknown>
  cuDNN Build Version          : None
  cuDNN Version                : None
  NCCL Build Version           : None
  NCCL Runtime Version         : None
  cuTENSOR Version             : None
  cuSPARSELt Build Version     : None
  Device 0 Name                : NVIDIA GeForce RTX 3060 Laptop GPU
  Device 0 Compute Capability  : 86
  Device 0 PCI Bus ID          : 0000:01:00.0
  ```
  
  
  ### Additional Information
  
  _No response_