tests: decouple Kafka topic helper from Sarama

[3AceShowHand]

What to build

Replace the Kafka topic administration helper used by integration tests with a non-Sarama implementation. Preserve its command-line interface and behavior so existing integration test scripts do not need client-specific logic.

Acceptance criteria

• The helper and its tests do not import or refer to Sarama.
• The helper can create a topic with the requested max.message.bytes value.
• The helper can alter max.message.bytes for an existing topic.
• Existing integration test scripts continue to use the same flags and behavior.
• Kafka integration cases that use the helper pass.

Blocked by

None - can start immediately.