[Fix] Pause ConfigNode Pipe events polled after stop

[Caideyipi]

Description

When STOP PIPE finishes while a ConfigNode task is blocked in source.supply(), the task can still transfer events created afterward. This causes IoTDBPipeLifeCycleIT.testLifeCycleWithHistoryDisabled to see root.ln0 on the receiver while the Pipe is stopped.

Check the stop flag before polling and again after the source returns. Keep a fetched event in lastEvent so restarting the Pipe transfers and commits it once. If the task was dropped during polling, release the fetched event without committing it.

Add deterministic regression tests for a stopped task, stopping during a blocked poll followed by restart, and dropping during a blocked poll.

Validation

• The two stop regression tests fail against the original implementation.
• PipeConfigNodeSubtaskTest and PipeConfigNodeSubtaskExecutorTest: 8 tests passed.
• IoTDBPipeLifeCycleIT#testLifeCycleWithHistoryDisabled: passed with two ScalableSingleNodeMode clusters using the rebuilt ConfigNode jar. The initial local attempt exhausted Windows committed memory during node startup; the rerun passed with bounded JVM heaps.
• ConfigNode main and test sources compile in both English and Chinese locales.
• Spotless and git diff --check passed.