use hasPresence instead of proto3 checks

[ubiquitousbyte]

What

See #3925

Checklist

Please answer the questions with Y, N or N/A if not applicable.

• [Y] Contains customer facing changes? Including API/behavior changes
• [N] Is this change gated behind config(s)?
• [N] Did you add sufficient unit test and/or integration test coverage for this PR?
  • If not, please explain why it is not required
• [N/A] Does this change require modifying existing system tests or adding new system tests?
  • If so, include tracking information for the system test changes
• [N] Must this be released together with other change(s), either in this repo or another one?
  • If so, please include the link(s) to the changes that must be released together

References

#3569

Test & Review

Haven't tested it. Only found the bug by using the FileStreamSinkConnector with a Protobuf message similar to the one described in the issue and seeing that field-presence tracking is not respected by Kafka Connect.

Open questions / Follow-ups

Should this be gate-kept by a feature flag?

Review stakeholders

@rayokota

[confluent-cla-assistant]

🎉 All Contributor License Agreements have been signed. Ready to merge.
✅ ubiquitousbyte
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[Copilot]

Pull Request Overview

This PR updates the protobuf converter to use the hasPresence() method instead of checking for proto3Optional() when determining if a field is optional. This change addresses field-presence tracking issues in Kafka Connect when working with Protobuf messages.

• Replaces proto3-specific optional check with a more general presence check
• Improves field-presence handling for protobuf messages in Kafka Connect

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[rayokota]

/sem-approve

[rayokota]

/sem-approve