lib: updates for cmetrics and monkey (v4.0 backport)

[edsiper]

Backport of #10870

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Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.

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✨ Finishing Touches

🧪 Generate unit tests

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch 4.0-lib-updates-20250910

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