Streaming -- validate user's responses

[squidarth]

Describe the bug

If the user yields some complex object that is not bytes or string in a generator response, it can lead to strange errors. For instance, if you yield a numpy array, you get this exception:

Aug 16 6:14:28pm
Exception while reading stream response: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

Traceback (most recent call last):
  File "/app/model_wrapper.py", line 249, in write_response_to_queue
    async for chunk in generator:
  File "/app/model_wrapper.py", line 351, in _convert_generator_to_async
    if chunk == FINAL_GENERATOR_VALUE:
ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

To Reproduce

Yield a numpy array from a generator returned from the predict method.

Expected behavior

We should throw exception if the user yields something that isn't bytes or a string.

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Desktop (please complete the following information):

• OS: [e.g. macOS]
• Environment versions [e.g. python versions, framework/package versions]
• Truss version [e.g. 22]

Additional context
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