test(sagemaker): add HyperPod integration tests

[aws-ajangg]

Problem

• HyperPod SSH connection flows lack integration test coverage. There are no tests verifying that the end-to-end workflows (deeplink → connection, side panel → connection, space lifecycle, server routes) work correctly when components are wired together.

Solution

• Add integration tests for HyperPod SSH connections following existing patterns in packages/core/src/testInteg/.

Integration tests coverage:

• Deeplink connection flow (URI arrives → prepareDevEnvConnection → launch IDE)
• Side panel (LC) connection flow (click → prepareDevEnvConnection → launch IDE)
• Space lifecycle (stop with confirmation, start invalid/error, connect-to-stopped with wait)
• Server routes with real HTTP server (/get_hyperpod_session, /get_hyperpod_session_async)
• Multi-IDE support (VS Code smhp_, Cursor smhpc_, Kiro sagemaker-ssh-kiro)
• Error paths (remote workspace rejection, kubectl timeout, expired credentials)

Note:

• Unit test added for WriteQueue sequential write serialization (previously missing coverage).

Testing

• Ran locally and passed with: npm run testInteg -w packages/toolkit

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• Treat all work as PUBLIC. Private feature/x branches will not be squash-merged at release time.
• Your code changes must meet the guidelines in CONTRIBUTING.md.
• License: I confirm that my contribution is made under the terms of the Apache 2.0 license.

[amazon-inspector-ohio]

⏳ I'm reviewing this pull request for security vulnerabilities and code quality issues. I'll provide an update when I'm done

[amazon-inspector-ohio]

✅ I finished the code review, and didn't find any security or code quality issues.