feat: add cloning fail fast check

[zepfred]

No description provided.

[Copilot]

Pull request overview

This PR adds a fail-fast validation to the deep-cloning subsystem to prevent invalid configurations where a basic planning variable is marked for deep cloning but its value type is not deep-clonable, and it adds a regression test plus minimal testdomain classes to cover the scenario.

Changes:

• Add a fail-fast IllegalStateException in DeepCloningUtils.isFieldDeepCloned(...) for @PlanningVariable + @DeepPlanningClone fields whose type is not deep-cloned.
• Introduce a dedicated invalid testdomain entity/solution that reproduces the configuration mistake.
• Add a unit test asserting the new error message guidance.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
core/src/main/java/ai/timefold/solver/core/impl/domain/solution/cloner/DeepCloningUtils.java	Adds the new validation and a helper to detect basic planning variables via field/getter annotations.
core/src/test/java/ai/timefold/solver/core/impl/domain/solution/cloner/AbstractSolutionClonerTest.java	Adds a regression test asserting fail-fast behavior and message content.
core/src/test/java/ai/timefold/solver/core/testdomain/clone/deepcloning/field/invalid/TestdataInvalidEntityProvidingSolution.java	New test solution used to trigger the invalid deep-clone configuration.
core/src/test/java/ai/timefold/solver/core/testdomain/clone/deepcloning/field/invalid/TestdataInvalidEntityProvidingEntity.java	New test entity with @PlanningVariable and a deliberately invalid @DeepPlanningClone setup.

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.