fix(signals): run onDestroy outside of injection context

[rainerhahnekamp]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ngrx/platform/blob/main/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
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PR Type

The Signal Store saves the injection context upon instantiation and re-uses it in the onDestroy hook.

If the Store is provided in root, any test with an onDestroy hook fails with the error message: NG0205: Injector has already been destroyed.

This PR runs onDestroy outside of the injection context.

Since this will break any code which depends on the injection context in onDestroy, there will be follow-up (breaking change) feature which will provide the injection context before the hook is executed.

Discussed in: #4196

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

Any test with a store providedIn: root fails.

Closes #

What is the new behavior?

onDestroy runs outside of the injection context.

Does this PR introduce a breaking change?

[x] Yes
[ ] No

There will be a feature PR which re-enables the injection context, but in a different way.

Other information

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