[fix][fn] Ack late tuples in window functions under ATLEAST_ONCE

[Dream95]

Fixes #26577

Motivation

Window functions ack ATLEAST_ONCE records in processWindow, after the window fires. A late tuple (timestamp behind the watermark) is not added to WindowManager, so that ack never happens.
The message stays unacked, gets redelivered, and can push the consumer toward maxUnackedMessages.
ATMOST_ONCE already acks at the start of process(), so it is unaffected.

Modifications

WindowFunctionExecutor.process() acks late tuples when the guarantee is ATLEAST_ONCE.
If lateDataTopic is not set, ack after the existing "will not be processed" log. If it is set, ack in thenAccept after the late-data send succeeds. A failed send leaves the record unacked.

Verifying this change

• Make sure that the change passes the CI checks.
  This change added tests and can be verified as follows:
• testLateTupleAckedWithAtleastOnce covers the no-late-data-topic case
• testLateTupleAckedAfterLateDataSend checks that ack waits for a successful send
• testLateTupleNotAckedWhenLateDataSendFails checks that a failed send does not ack

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