[release-19.0] smartconnpool: Better handling for idle expiration (#17757)

[vitess-bot]

Description

This is a backport of #17757

[vitess-bot]

Hello @vmg, there are conflicts in this backport.

Please address them in order to merge this Pull Request. You can execute the snippet below to reset your branch and resolve the conflict manually.

Make sure you replace origin by the name of the vitessio/vitess remote

git fetch --all
gh pr checkout 17779 -R vitessio/vitess
git reset --hard origin/release-19.0
git cherry-pick -m 1 057bcc92191ccb29fbf45fad3c1cf33acc508f80

[vitess-bot]

Hello! 👋

This Pull Request is now handled by arewefastyet. The current HEAD and future commits will be benchmarked.

You can find the performance comparison on the arewefastyet website.

[vitess-bot]

Review Checklist

Hello reviewers! 👋 Please follow this checklist when reviewing this Pull Request.

General

• Ensure that the Pull Request has a descriptive title.
• Ensure there is a link to an issue (except for internal cleanup and flaky test fixes), new features should have an RFC that documents use cases and test cases.

Tests

• Bug fixes should have at least one unit or end-to-end test, enhancement and new features should have a sufficient number of tests.

Documentation

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• There should be a comment at the top of each new or modified test to explain what the test does.

New flags

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Backward compatibility

• Protobuf changes should be wire-compatible.
• Changes to _vt tables and RPCs need to be backward compatible.
• RPC changes should be compatible with vitess-operator
• If a flag is removed, then it should also be removed from vitess-operator and arewefastyet, if used there.
• vtctl command output order should be stable and awk-able.

[deepthi]

v19 is EOL soon, and this is a performance improvement, not a critical bug fix.