Stop iterating response body on error for bidirectional streams

[SamRemis]

Issue #, if available:
#657

Description of changes:
On bidirectional HTTP/2 streams, the CRT only signals response body completion when both sides of the stream have sent END_STREAM. When the server returns a non-2xx response (e.g., 429 ThrottlingException), the client side is still open sending events, so get_next_response_chunk() hangs forever waiting for a completion signal that never comes.

This PR updates the CRT HTTP client to break out of the chunks() loop after the first chunk when the response status is >= 400. The error body is already fully buffered by the CRT at that point, allowing the error to be deserialized and raised.

Note: this is a workaround for the CRT not signaling response body completion on half-closed HTTP/2 streams. A complete fix requires the CRT breaking this loop on a half-closed stream. For typical error responses, the body arrives in a single chunk and is fully available before this code runs, but this code will truncate any error response in 2 or more chunks.

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[SamRemis]

Note - the CRT team is aware of this issue and is working on it in tandem. Hopefully they fix this upstream and we can never merge this.

[SamRemis]

Closing in favor of #672