[Java] Support batch acknowledgements for PushConsumer

[qianye1001]

Which Issue(s) This PR Fixes

Fixes #1325

Brief Description

The Java gRPC PushConsumer currently sends one acknowledgement RPC for every successfully consumed message even though AckMessageRequest supports repeated entries. Under a high consume rate, these one-entry requests add substantial client and Proxy overhead.

This change introduces one acknowledgement batcher per PushConsumer:

• Batches are partitioned by endpoint and topic to match the request routing and protocol constraints.
• A batch is flushed after 5 seconds or when it reaches 1,024 messages.
• Only messages consumed within 25 seconds of receive/decode are eligible. Slow messages use the existing immediate acknowledgement path.
• FIFO acknowledgements remain immediate because subsequent ordered messages depend on them.
• Lite consumers retain the existing immediate acknowledgement behavior.
• Multi-entry responses are mapped back to each message by message ID. Missing or failed results use the existing delayed individual retry path; invalid receipt handles preserve the existing no-retry behavior.
• PushConsumer shutdown waits for consumption to finish and then flushes pending and in-flight acknowledgement batches.
• ACK interceptors still receive all messages included in each batch.

The current RocketMQ Proxy protocol and batch-ACK path already accept repeated entries, so this change does not require a protocol update.

At approximately 8,000 TPS in the medium 2B workload, two controlled candidate runs averaged about 20.4 entries per ACK RPC, reducing ACK RPC volume by approximately 95.1%. Total Java consumer CPU decreased by approximately 20.6%, while throughput remained unchanged. A separate single-topic validation observed requests with exactly 1,024 entries.

How Did You Test This Change?

• zsh -ic 'javaswitch 11 >/dev/null && mvn -f java/pom.xml -pl client -am test'
  • 304 tests run
  • 0 failures
  • 0 errors
  • 1 skipped
• Checkstyle: 0 violations
• SpotBugs: 0 errors or warnings
• Verified the compiled batcher class remains Java 8 compatible (major version: 52).
• Ran an end-to-end Kubernetes smoke test against a two-Broker/two-Proxy deployment with batch ACK enabled.
• Ran a medium 2B A-B-B-A comparison with 1,000 topics, 1,000 groups, 2,000 producers, 2,000 consumers, 4 KiB messages, 120 seconds warm-up, and 300 seconds sampling per round.

Metric	Baseline mean	Batch ACK mean	Change
Send TPS	7,981.0	7,981.5	+0.01%
Consumer total CPU	3.446 cores	2.736 cores	-20.59%
Consumer CPU p95	3.658 cores	2.975 cores	-18.67%
Proxy total CPU	10.998 cores	9.052 cores	-17.70%
E2E latency p99	21.682 ms	20.515 ms	-5.38%

[codecov-commenter]

Codecov Report

❌ Patch coverage is 76.04167% with 46 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.24%. Comparing base (4076e2b) to head (a5c68e8).
⚠️ Report is 166 commits behind head on master.

Files with missing lines	Patch %	Lines
...q/client/java/impl/consumer/AckMessageBatcher.java	81.45%	21 Missing and 7 partials ⚠️
...mq/client/java/impl/consumer/PushConsumerImpl.java	0.00%	12 Missing ⚠️
...mq/client/java/impl/consumer/ProcessQueueImpl.java	63.63%	1 Missing and 3 partials ⚠️
...cketmq/client/java/impl/consumer/ConsumerImpl.java	88.88%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1326      +/-   ##
============================================
+ Coverage     53.26%   63.24%   +9.97%     
- Complexity      651      856     +205     
============================================
  Files           208      109      -99     
  Lines         14303     4807    -9496     
  Branches       5845      390    -5455     
============================================
- Hits           7619     3040    -4579     
+ Misses         6308     1558    -4750     
+ Partials        376      209     -167     

Flag	Coverage Δ
cpp	?
golang	?
java	63.24% <76.04%> (+1.55%)	⬆️
rust	?

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[RockteMQ-AI]

Summary

Introduces AckMessageBatcher to batch PushConsumer acknowledgements by (endpoints, topic), reducing per-message RPC overhead. The design is clean: batches are flushed either when the size threshold is reached or when a delay timer expires. Partial failures (MULTIPLE_RESULTS) are correctly mapped back to individual message futures, and missing results default to INTERNAL_ERROR so the caller can retry. FIFO and lite-consumer messages correctly bypass batching to preserve ordering guarantees.

The retry path (ackMessageLater) correctly forces batchable=false to prevent re-batching of failed messages, and flushAndClose() provides a graceful shutdown mechanism.

Comprehensive test coverage (7 test cases) validates the key scenarios.

LGTM.

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