[fix][io] Fix delayed acknowledgment for offset 0 in Kafka Connect Adapter

[sandeep-mst]

Fixes #23

Motivation

PulsarKafkaSinkTaskContext.currentOffsets() was filtering out offsets equal to 0 by only including values greater than 0. This caused the first record in a partition, whose offset can legitimately be 0, to be omitted from the offsets snapshot returned to KafkaConnectSink#flush(). As a result, the acknowledgment for that record was not flushed until a later record with a non-zero offset was processed.

This change ensures that offset 0 is treated as a valid offset and is included in the current offsets map, so the first record can be acknowledged without waiting for another record.

Modifications

The offset filter in PulsarKafkaSinkTaskContext.currentOffsets() was changed from:
if (offset > 0) {
to:
if (offset >= 0) {

This includes records with offset 0 in the returned snapshot.
A assertion was added to existing offsetTest in KafkaConnectSinkTest to verify that currentOffsets() contains that record and reports offset 0 correctly.

Verifying this change

• Make sure that the change passes the CI checks.

This change added tests and can be verified as follows:

• org.apache.pulsar.io.kafka.connect.KafkaConnectSinkTest#offsetTest (updated existing test)

Does this pull request potentially affect one of the following parts:

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• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment

Documentation

• doc
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Matching PR in forked repository

PR in forked repository:
cognitree#6

[sandeep-mst]

@dlg99, @lhotari Please let me know if anything else is required on this PR.