[ISSUE #135] Add gRPC connector on LiteSimpleConsumer with downstream ack and sub-topic throttling

[lizhimins]

Closes #135

内容

新增独立模块 flink-connector-rocketmq-grpc（及 SQL fat-jar flink-sql-connector-rocketmq-grpc），基于 rocketmq-client-java 5.2.1+ 的 LiteSimpleConsumer（Pop 模型）：

Source

• bindTopic 主 lite topic 泛化订阅，broker 做消息级负载均衡，不做 split 分区；
• 每 subtask 单个共享 consumer + fetch-concurrency 个并发 receive() 长轮询线程，接收失败指数退避；
• source 永不 ack，产出 AckableMessage<OUT>（payload + 可序列化、免凭据的 RocketMQReceiptHandle），配套专用 TypeInformation/TypeSerializer（不走 Kryo）。

下游 ack / 限流（DataStream-only）

• RocketMQLiteAckClient：每 TM 引用计数池化，按 handle 的路由三元组 (endpoint, namespace, consumerGroup) 维护同组 consumer 池；ack RPC 有界指数退避重试，INVALID_RECEIPT_HANDLE 容忍为 warn（消息重投，at-least-once）；
• 两种接线：继承 RocketMQAckProcessFunction 直接 ack()/changeInvisibleDuration()，或 MessageThrottlePolicy<T> + RocketMQThrottleProcessFunction<T>（内置 maxDeliveryAttempt=16、maxInvisibleDuration=30min 安全阀）；
• 凭据不入数据流：静态 AK/SK 或可插拔 CredentialsResolver（TM 本地按 endpoint 解析）；
• SDK internal 依赖收敛到唯一的 @Internal 适配类 RocketMQReceiptHandleCodec。

其它

• invisible-duration 续期策略（背压时对未 emit 的队内消息续期，emit 后冻结 handle）；
• gRPC producer sink 与 rocketmq-grpc SQL connector；
• 设计文档 docs/grpc-connector.md：动机、架构、语义、决策与被否决的备选方案。

验证

• 模块单测 50 个全部通过（serializer round-trip、引用计数、codec、throttle policy 分支等）；
• 真实 RocketMQ 5.x 集群 E2E：限流 defer（5 条消息 ~10s 后重投并 ack）与背压续期（renewals=102、duplicates=0/60）均 PASS；
• mvn spotless:check clean package（JDK 11/17）全部 BUILD SUCCESS。

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What

Adds a separate module flink-connector-rocketmq-grpc (plus the SQL fat-jar flink-sql-connector-rocketmq-grpc) built on rocketmq-client-java 5.2.1+ LiteSimpleConsumer (Pop model):

Source

• Binds one main lite topic with a wildcard subscription; the broker performs message-level load balancing, so there is no split partitioning.
• Each subtask runs one shared consumer with fetch-concurrency concurrent receive() long-poll workers; receive failures back off exponentially.
• The source never acks. It emits AckableMessage<OUT> — the payload plus a serializable, credential-free RocketMQReceiptHandle — with dedicated TypeInformation/TypeSerializer (no Kryo fallback).

Downstream ack / throttling (DataStream-only)

• RocketMQLiteAckClient: per-TaskManager reference-counted pool keyed by the handle routing triple (endpoint, namespace, consumerGroup); ack RPCs retry with bounded exponential backoff, and INVALID_RECEIPT_HANDLE is tolerated as a warning (redelivery, at-least-once).
• Two wirings: extend RocketMQAckProcessFunction and call ack()/changeInvisibleDuration() directly, or implement MessageThrottlePolicy<T> with RocketMQThrottleProcessFunction<T> (built-in safety valves: maxDeliveryAttempt=16, maxInvisibleDuration=30min).
• Credentials never travel in the stream: static AK/SK or a pluggable CredentialsResolver resolved locally per TaskManager and endpoint.
• SDK-internal usage is confined to a single @Internal adapter, RocketMQReceiptHandleCodec.

Other

• Invisible-duration renewal policy (renews queue-resident messages under backpressure; handles are frozen once emitted).
• gRPC producer sink and the rocketmq-grpc SQL connector.
• Design document docs/grpc-connector.md: motivation, architecture, semantics, decisions and rejected alternatives.

Verification

• 50 module unit tests pass (serializer round-trips, reference counting, codec, throttle policy branches, etc.).
• E2E against a real RocketMQ 5.x cluster: throttle defer (5 messages redelivered after ~10s then acked) and backpressure renewal (renewals=102, duplicates=0/60) both PASS.
• mvn spotless:check clean package succeeds on JDK 11 and 17.