Pipe: Fix tablet event alignment and row count handling #29825

Job	Run time
unit-test (17, ubuntu-latest, datanode)	27m 11s
unit-test (17, ubuntu-latest, others)	15m 35s
unit-test (17, windows-latest, others)	20m 22s
unit-test (17, windows-latest, datanode)	27m 48s
	1h 30m 56s

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