test(amber): add unit test coverage for ExecutionUtils

[aglinxinyuan]

Task Summary

ExecutionUtils (amber/src/main/scala/org/apache/texera/amber/engine/architecture/controller/execution/ExecutionUtils.scala) provides three pure aggregator functions used to roll up runtime statistics across regions/operators/ports, but currently has no unit tests. Add ExecutionUtilsSpec covering:

• aggregateStates — empty, all-completed, all-terminated, has-running, all-uninitialized, all-paused, all-ready (maps to RUNNING), mixed (UNKNOWN)
• aggregatePortMetrics — empty, single mapping, sum-on-same-port, group-by-port-id
• aggregateMetrics — empty defaults, scalar sum + per-port merge across operators, internal-port filtering

Priority

P3 – Low

Task Type

• Testing / QA