test: add GoogleTest support to v2

[tkilias]

Summary

• Add GoogleTest to the v2 Bazel module and migrate functional v2 tests from custom assert-based mains.
• Make GoogleMock available for future interaction-based tests without introducing artificial mocks.
• Document GoogleTest, GoogleMock, and Google Benchmark conventions for v2.
• Preserve specialized ELF, dynamic-loading, and header-order tests.
• Address SonarCloud coverage and exception-quality findings.
• Add the required unreleased changelog entry.

Validation

• Full v2 Bazel suite: 17/17 tests passed with Bazel 8.3.1.
• Waitable queue benchmark built and ran successfully.
• clang-format Bazel validation passed.
• clang-tidy was not completed because clang-tidy-22 is unavailable in the environment.

Fixes #64

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-23T15:18:36.991102Z	d26a219	PR opened

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[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: d26a219412

ℹ️ About Codex in GitHub

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• Open a pull request for review
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• Comment "@codex review".

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud