Demangle pytorch and tensorflow dependencies

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Issue Description

Currently our dependencies for the deep explainer are mangled together somewhere deep down. This best visible when running the notebook notebooks/image_examples/image_classification/PyTorch Deep Explainer MNIST example.ipynb without tf_keras installed, then one gets an error. This is completely counter intuitive since this notebook just needs pytorch related dependencies. We should definitely get this into a state where pytorch and tensorflow code can coexist without the other framework being installed.

Minimal Reproducible Example

pip uninstall tf_keras

then run `notebooks/image_examples/image_classification/PyTorch Deep Explainer MNIST example.ipynb`

then this throws an error in the cell



# since shuffle=True, this is a random sample of test data
batch = next(iter(test_loader))
images, _ = batch

background = images[:100]
test_images = images[100:103]

e = shap.DeepExplainer(model, background)
shap_values = e.shap_values(test_images)
``

Traceback

---------------------------------------------------------------------------
ModuleNotFoundError                       Traceback (most recent call last)
File ~/programming/github/shap_master/.venv/lib/python3.10/site-packages/transformers/activations_tf.py:22
     21 try:
---> 22     import tf_keras as keras
     23 except (ModuleNotFoundError, ImportError):

ModuleNotFoundError: No module named 'tf_keras'

During handling of the above exception, another exception occurred:

ValueError                                Traceback (most recent call last)
File ~/programming/github/shap_master/.venv/lib/python3.10/site-packages/transformers/utils/import_utils.py:1472, in _LazyModule._get_module(self, module_name)
   1471 try:
-> 1472     return importlib.import_module("." + module_name, self.__name__)
   1473 except Exception as e:

File /usr/lib/python3.10/importlib/__init__.py:126, in import_module(name, package)
    125         level += 1
--> 126 return _bootstrap._gcd_import(name[level:], package, level)

File <frozen importlib._bootstrap>:1050, in _gcd_import(name, package, level)

File <frozen importlib._bootstrap>:1027, in _find_and_load(name, import_)
...
   1476         f" traceback):\n{e}"
   1477     ) from e

RuntimeError: Failed to import transformers.modeling_tf_utils because of the following error (look up to see its traceback):
Your currently installed version of Keras is Keras 3, but this is not yet supported in Transformers. Please install the backwards-compatible tf-keras package with `pip install tf-keras`.

Expected Behavior

should work without any tensorflow dependencies

Bug report checklist

• I have checked that this issue has not already been reported.
• I have confirmed this bug exists on the latest release of shap.
• I have confirmed this bug exists on the master branch of shap.
• I'd be interested in making a PR to fix this bug

Installed Versions

master