Close request when initial response fails and propagate error

[alextwoods]

Description of changes:
This fixes an issue where event stream initial response failures cause the stream to hang. There are two issues:

1. The response body will not be closed until the request body gets closed (because the h2 streams will be left open). To signal the server to close the connection, we need to also close the request body to end it. This is accomplished by checking for error status codes and setting the response future to an exception. If the response is not closed, the deserialize_error methods will hang forever trying to read the body.
2. We were incorrectly not calling the done method on the asyncio response_future and so were not setting the exception in it correclty.

There may be better ways to ensure the request body gets closed on an error in initial request.

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[nateprewitt]

What actually gets surfaced to the end user with the stack trace here? Is it only the message being passed to the base Exception constructor? Ideally we have more context if we can.

[alextwoods]

This exception gets caught in the AWSCRTHTTPClient.send method, which then closes the request body and returns the response upwards. The client code then deserializes the response using its deserializers and will create the appropriate service exception. An example for an expired security token:

Traceback (most recent call last):
  File "/Users/alexwoo/python/test-lexruntime/lexruntime/client.py", line 595, in _execute_operation
    return await self._handle_execution(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/alexwoo/python/test-lexruntime/lexruntime/client.py", line 751, in _handle_execution
    return await self._finalize_execution(interceptor_chain, output_context)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/alexwoo/python/test-lexruntime/lexruntime/client.py", line 1003, in _finalize_execution
    raise context.response
  File "/Users/alexwoo/python/test-lexruntime/lexruntime/client.py", line 717, in _handle_execution
    raise output_context.response
  File "/Users/alexwoo/python/test-lexruntime/lexruntime/client.py", line 916, in _handle_attempt
    output = await deserialize(response_context.transport_response, config)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/alexwoo/python/test-lexruntime/lexruntime/deserialize.py", line 403, in _deserialize_start_conversation
    raise e
lexruntime.models.UnknownApiError: ExpiredTokenException: The security token included in the request is expired