#6949 Fix Netty streaming completion guard

[arnabnandy7]

Motivation and Context

Fixes #6949.

NettyNioAsyncHttpClient could suppress a channel-inactive fallback error when STREAMING_COMPLETE_KEY was true but RESPONSE_COMPLETE_KEY was not yet true. For AsyncResponseTransformer.toPublisher(), observing the final HTTP content does not necessarily mean the caller-visible response publisher has received a terminal signal, so this could leave subscribers waiting indefinitely.

Modifications

Changed ResponseHandler.notifyIfResponseNotCompleted() to treat only RESPONSE_COMPLETE_KEY=true as sufficient proof that the response has completed.

Added a regression test covering the problematic state where streaming is marked complete, response finalization has not happened, and the channel becomes inactive. The test verifies that an IOException is surfaced, the execute future completes exceptionally, and the channel is released.

Added a changelog entry for the Netty NIO Async HTTP Client bug fix.

Testing

Ran:

.\mvnw.cmd -pl http-clients\netty-nio-client -Dtest=PublisherAdapterTest test

Result: passed, 6 tests.

Also ran:

.\mvnw.cmd -pl http-clients\netty-nio-client -am test

This failed before reaching the Netty module in core/annotations during SpotBugs.

Also ran:

.\mvnw.cmd -pl http-clients\netty-nio-client test

This failed due to unrelated local runtime/tooling issues: WireMock certificate generation was unsupported on this runtime, and JaCoCo reported Unsupported class file major version 70.

Ran:

git diff --check

Result: passed.

Screenshots (if appropriate)

N/A

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Checklist

• I have read the [CONTRIBUTING](https://github.com/aws/aws-sdk-java-v2/blob/master/CONTRIBUTING.md) document
• Local run of mvn install succeeds
• My code follows the code style of this project
• My change requires a change to the Javadoc documentation
• I have updated the Javadoc documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed
• I have added a changelog entry. Adding a new entry must be accomplished by running the scripts/new-change script and following the instructions. Commit the new file created by the script in .changes/next-release with your changes.
• My change is to implement 1.11 parity feature and I have updated [LaunchChangelog](https://github.com/aws/aws-sdk-java-v2/blob/master/docs/LaunchChangelog.md)

License

• I confirm that this pull request can be released under the Apache 2 license