text: Title: `data.create_image_fetcher` should be private
  Body: ### Description:
  
  https://github.com/scikit-image/scikit-image/blob/c90bfccbc930262eebd1149b10660bfa4f56ec61/skimage/data/__init__.pyi#L16
  
  has no docstring and is probably intended as a private initializer for pooch. So remove it from the PYI file and probably add an underscore to the function name to be totally explicit about it. :wink: 
  
  ### Way to reproduce:
  
  ```python
  import skimage as ski
  assert ski.data.create_image_fetcher.__doc__   # passes
  ```
  
  ### Version information:
  
  ```Shell
  3.10.10 (main, Mar  5 2023, 22:26:53) [GCC 12.2.1 20230201]
  Linux-6.2.7-arch1-1-x86_64-with-glibc2.37
  scikit-image version: 0.21.0rc0.dev0+git20230323.c90bfccbc
  numpy version: 1.24.1
  ```
  