add unit test coverage for worker managers (Statistics/Serialization/Pause)

[aglinxinyuan]

Add a focused WorkerManagersSpec covering the worker-side state managers under amber/.../worker and amber/.../worker/managers:

• StatisticsManager — defaults, per-port input/output count+size accumulation, negative-size rejection, processing-time accumulation, idleTime = total - data - control, current-time-before-start rejection
• SerializationManager.registerSerialization / applySerialization — no-op without callback, single-fire then clear, latest-overwrites-previous
• PauseManager — initial isPaused, global pause disables all data channels (control channels untouched), resume reactivates when no pauses remain, multi-pause aggregation (resume keeps paused if other global pause active), specific-channel pause/resume layered with global pauses

EmbeddedControlMessageManager is intentionally not covered here — it requires the full InputManager + ECM infrastructure and is best exercised by an integration test.

Priority

P3 - Low

Task Type

• Testing / QA