Closes #6181: DB Query can cause timeout

[Miraeld]

Description

On a site with many many private posts, any action that involves post cache clearing will result in a timeout error.
DB Queries have been optimised to make it more responsive and quicl.

Fixes #6181

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue).

Is the solution different from the one proposed during the grooming?

No

Checklists

Generic development checklist

• My code follows the style guidelines of this project, with adapted comments and without new warnings.
• I have added unit and integration tests that prove my fix is effective or that my feature works.
• The CI passes locally with my changes (including unit tests, integration tests, linter).
• Any dependent changes have been merged and published in downstream modules.
• If applicable, I have made corresponding changes to the documentation. Provide a link to the documentation.

Test summary

• I triggered all changed lines of code at least once without new errors/warnings/notices.
• I validated all Acceptance Criteria of the related issues. (If applicable, provide proof).
• I validated all test plan the QA Review asked me to.

[vmanthos]

This is working as expected as far as the feature goes.

NOTE

I haven't been able to reproduce the original issue although I tried to do so in different environments. Testing was mainly about preventing regressions.

TestRail report: testrail-report-540.pdf