smithy-http: stream aiohttp response bodies

[arandito]

Description

This PR updates AIOHTTPClient to stream response bodies instead of buffering the full payload before returning. This enables modeled streaming outputs to be consumed incrementally and aligns aiohttp response handling with the CRT transport.

The response body uses aiohttp’s raw chunk iterator and exposes close() so partially consumed responses can be released. Non-streaming responses continue to be consumed as a complete body during deserialization.

Testing

• Added unit test coverage for streaming and non-streaming responses, partial consumption cleanup, and response cleanup on marshalling failure.
• Ran make test-py - 1975 passed, 9 skipped.
• Generated bedrock runtime client with unreleased changes from Add async client transport cleanup #765 and confirmed that output streams now receive events incrementally for converse_stream operation. Also tested converse to confirm non-streaming operations remain functional.
• Generated sts and dynamo db clients to confirm query and aws json clients are functional as well.

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[Alan4506]

LGTM! Thanks @arandito