Add integration test for stall stream protection based on aws-sdk-rust#1202 (#3874)

## Motivation and Context
A follow-up on #3871, responding to [the review
feedback](https://github.com/smithy-lang/smithy-rs/pull/3871#pullrequestreview-2357786934)

## Testing
- Also confirmed that reverting the change in the above PR (so that
`BinLabel::Pending` becomes the top of the list) failed the integration
test added to this PR, as expected.
```
2024-10-10T19:06:56.417686Z TRACE aws_smithy_runtime::client::http::body::minimum_throughput::http_body_0_4_x: received poll pending
2024-10-10T19:06:56.417694Z DEBUG aws_smithy_runtime::client::http::body::minimum_throughput::http_body_0_4_x: current throughput: 0 B/s is below minimum: 1 B/s
thread 'user_polls_pending_followed_by_data_for_every_bin_in_throughput_logs' panicked at aws-smithy-runtime/tests/stalled_stream_download.rs:252:10:
response MUST NOT timeout: ThroughputBelowMinimum { expected: Throughput { bytes_read: 1, per_time_elapsed: 1s }, actual: Throughput { bytes_read: 0, per_time_elapsed: 1s } }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace


failures:
    user_polls_pending_followed_by_data_for_every_bin_in_throughput_logs
```

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