Add regression tests for default materialization in nested config schemas

[RonaldHensbergen]

Summary

Increase unit-test coverage for planner default handling in nested config schema structures.

Scope

• Add tests for nested object/array defaults in module configSchema.
• Verify defaults are materialized recursively without overwriting explicit profile values.
• Cover at least one edge case with partially provided nested input.

Acceptance criteria

• New tests fail before fix/coverage addition and pass after.
• Tests use existing unittest style and temporary fixtures.
• No behavior changes outside default materialization expectations.