Add test for uncovered parts of our code

[john-h-kastner-aws]

Describe the improvement you'd like to request

After #1494 we now have code coverage reports generated in CI. While overall our coverage percentage is high (over 80%) I noticed a few areas that were essentially untested while scrolling through the reports.

• Partial Evaluation commands in the CLI
• EST sub_entity_literals function
• json_schema.rs functions fully_qualify_type_references and conditionally_qualify_type_references
• Level validation (see Write more unit tests for level validation #1502)

Test coverage could improve in other areas, but these should be easy wins. Feel free to comment with other areas in need of testing, but try to limit the scope of this issue to function with essentially zero coverage

Describe alternatives you've considered

No response

Additional context

No response

Is this something that you'd be interested in working on?

• 👋 I may be able to implement this internal improvement
• ⚠️ This feature might incur a breaking change