fix: response model correctly wrapped for new instructor versions

[siillee]

Description

This PR fixes an issue we have with instructor 1.15.3 and possibly newer versions, regarding how the str respone model is handled. The fix is a simple Pydantic model wrapper around the response model.
In previous versions, instructor handled when the response model is not a Pydantic model. As of 1.15.3, they don't do that, and certain function calls fail, expecting a Pydantic model.

Acceptance Criteria

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Code refactoring
• Other (please specify):

Screenshots

Pre-submission Checklist

• I have tested my changes thoroughly before submitting this PR (See CONTRIBUTING.md)
• This PR contains minimal changes necessary to address the issue/feature
• My code follows the project's coding standards and style guidelines
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if applicable)
• All new and existing tests pass
• I have searched existing PRs to ensure this change hasn't been submitted already
• I have linked any relevant issues in the description
• My commits have clear and descriptive messages

DCO Affirmation

I affirm that all code in every commit of this pull request conforms to the terms of the Topoteretes Developer Certificate of Origin.