minor: optimize loops + presize in to/fromConnectData

[yuzawa-san]

What

• i was doing some more flame graph analysis on my deployment of kafka-connect and found some hotspots in the AvroData and ProtobufData classes, specifically on their toConnectData and fromConnectData implementations.
• these loops are quite hot and will benefit from simple iteration.
• additionally, i was able to presize some of the collections.
• i have another PR which optimizes the protobuf field hasField/getField which builds on this work.
• i also have a change in kafka for that Schema iteration MINOR: Optimize Struct.validate() field iteration apache/kafka#21281

cpu flamecharts (inset):

Checklist

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

• [N] Contains customer facing changes? Including API/behavior changes
• [N] Is this change gated behind config(s)?
  • List the config(s) needed to be set to enable this change
• [N/A] Did you add sufficient unit test and/or integration test coverage for this PR?
  • If not, please explain why it is not required
• [N] 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

JIRA: N/A

Test & Review

ran test suite

Open questions / Follow-ups

[confluent-cla-assistant]

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[Copilot]

Pull request overview

This PR optimizes performance in hot paths of Kafka Connect converters by improving loop iteration patterns and presizing collections.

Changes:

• Converted enhanced for-loops to indexed loops in fromConnectData and toConnectData methods across AvroData, ProtobufData, and JsonSchemaData classes
• Presized ArrayList allocations where collection sizes are known in ProtobufData

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
avro-data/src/main/java/io/confluent/connect/avro/AvroData.java	Optimized field iteration loops in fromConnectData and toConnectData methods by converting enhanced for-loops to indexed loops
protobuf-converter/src/main/java/io/confluent/connect/protobuf/ProtobufData.java	Presized ArrayList collections for ARRAY and MAP cases, and optimized field iteration loops in fromConnectData and toConnectData methods
json-schema-converter/src/main/java/io/confluent/connect/json/JsonSchemaData.java	Optimized field iteration loops in fromConnectData method for union and struct handling

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