fix(decoratormanager) applying decorators to a scalar using decorator sets

[dselman]

Closes #697

Fixes the DecoratorManager to allow it to apply decorators to models containing scalars.

Changes

• Adds a check for class declarations that do not contain a properties member (like scalars)
• Updates the unit test to include a scalar and a decorator command set that applies a decorator to a scalar

Flags

• @jonathan-casey we should add a similar unit test for Map declarations. We will have to think about how to add decorators to the key or value properties of a map.

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Author Checklist

• Ensure you provide a DCO sign-off for your commits using the --signoff option of git commit.
• Vital features and changes captured in unit and/or integration tests
• Commits messages follow AP format
• Extend the documentation, if necessary
• Merging to main from fork:branchname