Introduce dedicated validation functions for the testing scope

[liamcervante]

This is one of two PRs with alternate approaches to adding separate scope for the testing framework.

This PR:

• Introduces a new TestingReference struct to the addrs package.
• Introduces new functions into the scope and data validation packages that reference and use the new testing scope.

This is an alternative to #33339

[liamcervante]

We'll go with the implementation in #33339

[github-actions]

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