feat: Add @azure/functions-extensions-kafka package for KafkaRecord binding (#103)

[Tsuyoshi Ushio (TsuyoshiUshio)]

Summary

Add @azure/functions-extensions-kafka package that enables Node.js users to bind to raw Apache Kafka records (KafkaRecord type) with full metadata access via Protobuf deserialization.

Issue

Fixes #103
Relates to Azure/azure-functions-kafka-extension#612

Changes

New package: azure-functions-nodejs-extensions-kafka/

File	Description
types/index.d.ts	TypeScript interfaces: KafkaRecord, KafkaHeader, KafkaTimestamp, KafkaTimestampType
src/kafka/kafkaRecordDecoder.ts	Protobuf wire format decoder using protobufjs/minimal
src/kafka/kafkaRecordFactory.ts	ModelBindingData → KafkaRecord conversion (single + batch)
src/kafka/registerKafkaRecordFactory.ts	Register "AzureKafkaRecord" factory with ResourceFactoryResolver
src/index.ts	Auto-registers factory on import, re-exports types
test/kafkaRecordFactory.test.ts	8 tests: full record decode, null key/value, null leader epoch, null header value, single binding, batch binding, null content error, unknown timestamp type fallback

Follows the azure-functions-nodejs-extensions-servicebus pattern exactly.

No changes needed to azure-functions-nodejs-library or azure-functions-nodejs-worker.

Dependencies

• @azure/functions-extensions-base 0.3.0
• protobufjs ^7.4.0

Breaking Changes

None. New package — all existing Kafka bindings continue to work.

Testing

  KafkaRecordDecoder
    ✔ should decode a full record with all fields
    ✔ should handle null key and value
    ✔ should handle null leader epoch
    ✔ should handle null header value
  KafkaRecordFactory
    ✔ should build a KafkaRecord from single ModelBindingData
    ✔ should build KafkaRecord[] from batch ModelBindingData
    ✔ should throw when content is null
    ✔ should fallback unknown timestamp type to NotAvailable (0)

  8 passing (14ms)

User Experience

import { KafkaRecord } from '@azure/functions-extensions-kafka';

app.generic('KafkaTrigger', {
    trigger: { type: 'kafkaTrigger', topic: 'my-topic', brokerList: '%BrokerList%', consumerGroup: '$Default' },
    handler: async (record: KafkaRecord, context) => {
        context.log(`Topic: ${record.topic}, Partition: ${record.partition}`);
        const value = Buffer.from(record.value!).toString('utf-8');
    },
});

[Tsuyoshi Ushio (TsuyoshiUshio)]

E2E testing (Docker Compose + Kafka broker) is tracked separately in #105 due to the additional infrastructure complexity (Kafka KRaft broker setup, extension bundle dependency, topic auto-creation). This PR covers the package implementation, unit tests, CI build/lint/version integration, and sample app.