[KIP-482] Upgrade Transaction Apis to flexible versions

[PratRanj07]

Upgrade the following APIs to first flexible version

1. AddPartitionsToTxn(0 -> 3)
2. AddOffsetsToTxn(0 -> 3)
3. EndTxn(1 -> 3)

[confluent-cla-assistant]

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[Copilot]

Pull Request Overview

This PR upgrades three Admin APIs to their first flexible versions (version 3) as part of KIP-482 implementation: AddPartitionsToTxn, AddOffsetsToTxn, and EndTxn.

• Updates API version support from 0-1 to 0-3 for the three APIs
• Adds flexible versioning support with proper array count handling and tag skipping
• Updates mock handlers to support the new API versions

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/rdkafka_txnmgr.c	Updates response parsing to use array count functions and skip tags for flexible versioning
src/rdkafka_request.c	Upgrades API version support and adds flexible request formatting with tag handling
src/rdkafka_mock_handlers.c	Updates mock handlers to support new API versions and adds tag handling in responses

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[Copilot]

The tag skipping should be moved inside the partition loop (after line 2211) to properly handle tags for each partition entry, not after processing all partitions for a topic.

Suggested change

	rd_kafka_buf_skip_tags(rkbuf);
	}