print actual error message when failing to load a submodule

[kallewoof]

Great confusion in #2089 due to the actual underlying error being hidden behind importlib catching. This PR prints the error to console to help the user figure out what is going wrong.

[kallewoof]

-> % python
Python 3.12.3 | packaged by Anaconda, Inc. | (main, May  6 2024, 19:46:43) [GCC 11.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from huggingface_hub import hf_hub_download
Error importing huggingface_hub.file_download: partially initialized module 'charset_normalizer' has no attribute 'md__mypyc' (most likely due to a circular import)
Error importing huggingface_hub.file_download: partially initialized module 'charset_normalizer' has no attribute 'md__mypyc' (most likely due to a circular import)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: cannot import name 'hf_hub_download' from 'huggingface_hub' (/home/user/workspace/huggingface_hub/src/huggingface_hub/__init__.py). Did you mean: 'cached_download'?
>>> 
(ws) user@linux [13:07:49] [~/ws] 
-> % pip install -U charset-normalizer
Requirement already satisfied: charset-normalizer in /home/user/workspace/miniconda3/envs/ws/lib/python3.12/site-packages (3.3.2)
(ws) user@linux [13:09:44] [~/ws] 
-> % pip install --force-reinstall -U charset-normalizer
Collecting charset-normalizer
  Using cached charset_normalizer-3.3.2-cp312-cp312-manylinux_2_17_x86_64.manylinux2014_x86_64.whl.metadata (33 kB)
Using cached charset_normalizer-3.3.2-cp312-cp312-manylinux_2_17_x86_64.manylinux2014_x86_64.whl (141 kB)
Installing collected packages: charset-normalizer
  Attempting uninstall: charset-normalizer
    Found existing installation: charset-normalizer 3.3.2
    Uninstalling charset-normalizer-3.3.2:
      Successfully uninstalled charset-normalizer-3.3.2
Successfully installed charset-normalizer-3.3.2
(ws) user@linux [13:09:52] [~/ws] 
-> % python                                                                                                     
Python 3.12.3 | packaged by Anaconda, Inc. | (main, May  6 2024, 19:46:43) [GCC 11.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from huggingface_hub import hf_hub_download
>>>

[Wauplin]

That's a really nice finding @kallewoof, thanks a lot! We've already had some similar issues and I personally didn't know some import errors were hidden. Your PR will definitely save some headaches 🎉

[HuggingFaceDocBuilderDev]

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