feat: add Type hints for examples/keras_api_example.py

[Neerajpathak07]

Resolves #124

This PR adds a type hint for the examples file keras_api_example.py.
Optimizing the function from:-

def get_model():

def load_data():

to:-

def get_model() -> keras.Model:
  """Builds and returns the CNN model."""

def load_data() -> Tuple[
    Tuple[np.ndarray, np.ndarray],
    Tuple[np.ndarray, np.ndarray],
]:

[ryan112358]

Is lint complaining about this? If this fits under the line limit then I'd reverse this change

[Neerajpathak07]

Ran this locally and at the upstream CI for lint turns out it runs clean so no need to change this.

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[Neerajpathak07]

@ryan112358 Have updated the import orders on these as well.
PS:- the CI unit test error has also been resolved for all the downstream open PR's