add unit test coverage for ResultSchema

[aglinxinyuan]

Task Summary

Add ResultSchemaSpec pinning the canonical column layout of ResultSchema. Schema drift in this file silently breaks downstream readers, so a test pinning the column names and types is valuable:

• runtimeStatisticsSchema exposes the canonical columns in order
• runtimeStatisticsSchema pins the type of every column (operatorId STRING; time TIMESTAMP; inputTupleCnt/inputTupleSize/outputTupleCnt/outputTupleSize/dataProcessingTime/controlProcessingTime/idleTime LONG; numWorkers/status INTEGER)
• consoleMessagesSchema exposes a single STRING message column

Priority

P3 – Low

Task Type

• Testing / QA