test(amber): add unit test coverage for WorkflowScheduler

[aglinxinyuan]

Task Summary

WorkflowScheduler (amber/src/main/scala/org/apache/texera/amber/engine/architecture/controller/WorkflowScheduler.scala) wraps the cost-based generator and exposes the iterator-driven getNextRegions used by the controller, but has no dedicated unit tests of its own. Add WorkflowSchedulerSpec covering its public contract:

• updateSchedule populates getSchedule and physicalPlan from the input workflow
• The produced schedule covers every operator in the (post-update) physical plan
• getNextRegions exhausts the schedule and then returns an empty set
• The union of region sets pulled via getNextRegions matches getSchedule.getRegions

Priority

P3 – Low

Task Type

• Testing / QA