container_rebuild_test should use raw key value instead of state

liking to work on this

The merge request replaces the state service with direct access to its
underlying key/value collection in the container rebuild test module and its
functional test.

The now-unnecessary state cache refreshes have also been removed.

Local checks:

- PHP syntax checks passed.
- PHPCS passed.
- The functional test was not run locally because a functional test environment
is not configured. It is being exercised by CI.

AI-Generated: Yes. I used ChatGPT to help analyse and draft the initial change.
I reviewed the resulting diff and ran the reported checks locally.

Thanks! The merge request now uses the dedicated
`container_rebuild_test` key/value collection, with `count` as the key.
`RebuildScriptTest` has been updated accordingly.

Posting this as this may violate our AI policy

https://www.drupal.org/docs/develop/issues/issue-procedures-and-etiquett...

Thanks for pointing me to the policy. I have read it and would like to clarify how I used AI for this contribution.

I used ChatGPT to suggest an initial implementation and help draft the merge request text. I independently reviewed and understood every code change, ran the reported local checks, incorporated catch's feedback, and verified the updated result. I take full responsibility for the submitted work.

English is not my first language, and Drupal core issues can involve complex technical discussions. Before investing effort in a contribution, I use AI as a supporting tool to check that I have understood the problem correctly and to express my reasoning clearly in English. It does not replace my own technical judgement or responsibility; it helps me avoid misunderstandings caused by language.

If there is a specific part of the contribution or disclosure that does not meet the policy, please let me know and I will correct it.