fix(core): enforce correct kind on core resource models

[AlessandroPomponio]

Summary

Enforces that each core resource model only accepts its own kind value at validation time. Previously, pydantic would silently accept any valid CoreResourceKinds value for the kind field of any resource model; a mismatched kind could be deserialized without error. This change locks each model's kind field to a Literal of its specific enum member, so passing the wrong kind now raises a ValidationError.

High-level Changes

• CoreResourceKinds now inherits from str in addition to enum.Enum, enabling Literal constraints on enum members.
• The kind field on all five core resource models (DiscoverySpaceResource, OperationResource, SampleStoreResource, ActuatorConfigurationResource, DataContainerResource) is narrowed from the broad CoreResourceKinds type to Literal[CoreResourceKinds.<SPECIFIC_VALUE>].
• A commented-out dead enum member (ACTUATOR) is removed from CoreResourceKinds.
• New tests are added for each affected resource type to assert that providing a mismatched kind raises a pydantic.ValidationError.

Impact

Stricter model validation across all core resource types. Any code that previously constructed or deserialized a resource with an incorrect kind value will now fail fast with a clear validation error instead of producing a silently malformed object. No API or schema changes for correct usage.

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AI Disclosure: The code and this PR description were generated using IBM Bob and reviewed manually.