Add unit test coverage for machine-learning operator types (MachineLearningScorer, HyperParameters, SklearnMLOperatorDescriptor)

[aglinxinyuan]

Task Summary

Three machine-learning operator types under common/workflow-operator/machineLearning/ have no <srcClassName>Spec.scala.

Scope

Source class	Lines	What's currently un-pinned
machineLearning/Scorer/MachineLearningScorerOpDesc.scala	194	operatorInfo (Machine Learning Scorer); getOutputSchemas derives metric columns (regression vs classification); round-trip
machineLearning/sklearnAdvanced/base/HyperParameters.scala	69	generic config bag — parameter/attribute/value null defaults + parametersSource; @JsonProperty wire-keys + Include.NON_NULL serialization; round-trip
machineLearning/sklearnAdvanced/base/SklearnAdvancedBaseDesc.scala (SklearnMLOperatorDescriptor)	175	abstract base — operatorInfo derived from the subclass's getOperatorInfo (ADVANCED_SKLEARN_GROUP, two inputs training/parameter + one output); fixed getOutputSchemas; base-field defaults. Tested through a real concrete subclass (no stub — avoids the classpath-scanner concern)

Out of scope

No production-code changes. One <srcClassName>Spec.scala per source class.

Task Type

• Testing / QA