release-24.3: sqlliveness: prevent expiration regressions for sessions

[arulajmani]

Backport 2/2 commits from #160662 on behalf of @arulajmani.

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See individual commits for details.

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Release justification: fix a bug that can cause a node to shut down suddenly when sqlliveness queries get retried

[blathers-crl]

Thanks for opening a backport.

Before merging, please confirm that it falls into one of the following categories (select one):

• Non-production code changes. Includes test-only changes, build system changes, etc.
• Fixes for serious issues. Defined in the policy as correctness, stability, or security issues, data corruption/loss, significant performance regressions, breaking working and widely used functionality, or an inability to detect and debug production issues.
• Other approved changes. These changes must be gated behind a disabled-by-default feature flag unless there is a strong justification not to.

Add a brief release justification to the PR description explaining your selection.

Also, confirm that the change does not break backward compatibility and complies with all aspects of the backport policy.

All backports must be reviewed by the TL and EM for the owning area.

[blathers-crl]

✅ PR #160665 is compliant with backport policy

Confidence: high
Critical bug criteria met: [Stability or security issues]
Backward compatible: true
Explanation: This PR addresses the backport policy compliance for backporting changes to the 'release-24.3' branch. Firstly, the PR body includes a 'Release justification: fix a bug that can cause a node to shut down suddenly when sqlliveness queries get retried,' which permits an exemption from the standard backport policy requirements about critical bugs or feature flag gating. Such unexpected shutdowns of nodes are directly related to stability issues, qualifying as a critical bug fix under the provided policy. Furthermore, changes include modifications to non-production files (testing files), which are inherently exempt from critical bug or feature flag requirements. The primary production file changed, 'slinstance.go,' directly relates to the bug being addressed that potentially affects node stability. Finally, the changes are backward compatible as they do not remove any version gates or introduce breaking API changes, focusing primarily on bug fixes without altering existing functionality for users.

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[cockroach-teamcity]

This change is