feat(java): add batch consume support for PushConsumer

[qianye1001]

Summary

Add batch message consumption capability to the Java PushConsumer, allowing messages to be accumulated in a buffer and delivered in batches based on configurable policies.

• BatchMessageListener — new public API interface that receives List<MessageView> and returns a single ConsumeResult for the entire batch
• BatchPolicy — configurable batching strategy with Builder pattern and sensible defaults (32 msgs, 4MB, 5s). Flush triggers on any of: maxBatchSize, maxBatchBytes, maxWaitTime
• BatchConsumeService — Standard mode implementation with precise batch splitting (extractBatch respects both count and bytes limits simultaneously) and forward-progress guarantee (oversized single message still flushes)
• FifoBatchConsumeService — FIFO mode via inheritance with whole-batch retry semantics and single-batch-in-flight constraint. On failure, entire batch is retried until max attempts exhausted, then forwarded to DLQ
• ConsumeService enhanced — added close() lifecycle method, protected constructor for batch services (no NOOP listener hack), and accessor methods
• Config validation in builder: maxCacheMessageCount >= maxBatchSize, maxCacheMessageSizeInBytes >= maxBatchBytes
• Comprehensive tests using awaitility — 34 new test cases covering Standard/FIFO modes, retry, DLQ, concurrency, forward-progress, corrupted message handling, Builder validation
• BatchPushConsumerExample demonstrating usage

Key Design Decisions

Decision	Choice	Rationale
Batch result type	Single ConsumeResult per batch	Simple API; entire batch succeeds or fails together
Buffer scope	Global (mixed across ProcessQueues)	No PQ-based grouping; messages from all sources batch together
FIFO retry	Whole-batch retry	Preserves ordering guarantee; only one batch in-flight at a time
Class hierarchy	FifoBatchConsumeService extends BatchConsumeService	Clean separation via inheritance instead of if-else flag
Oversized messages	Forward-progress guarantee	Single message > maxBatchBytes still flushes as batch-of-one

Test plan

• BatchPolicyTest — 15 cases: constructor validation, Builder defaults, Builder custom values, invalid params
• BatchConsumeTaskTest — 6 cases: success, failure, exception, null return, unmodifiable list, batch size
• BatchConsumeServiceTest — 13 cases: maxBatchSize flush, maxBatchBytes flush, maxWaitTime flush, Standard failure, FIFO success, FIFO retry+DLQ, FIFO single-batch-in-flight, graceful shutdown, concurrent PQ submission, corrupted message discard, precise batch splitting, forward-progress, FIFO corrupted discard
• Full mvn -B package passes locally (JDK 11, 223 tests, 0 failures)

🤖 Generated with Claude Code

[codecov-commenter]

Codecov Report

❌ Patch coverage is 76.42857% with 66 lines in your changes missing coverage. Please review.
✅ Project coverage is 53.87%. Comparing base (4076e2b) to head (07fc971).
⚠️ Report is 122 commits behind head on master.

Files with missing lines	Patch %	Lines
...nt/java/impl/consumer/FifoBatchConsumeService.java	66.19%	21 Missing and 3 partials ⚠️
...client/java/impl/consumer/BatchConsumeService.java	84.72%	19 Missing and 3 partials ⚠️
...nt/java/impl/consumer/PushConsumerBuilderImpl.java	16.66%	8 Missing and 2 partials ⚠️
...mq/client/java/impl/consumer/PushConsumerImpl.java	30.76%	9 Missing ⚠️
...etmq/client/java/impl/consumer/ConsumeService.java	90.90%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1249      +/-   ##
============================================
+ Coverage     53.26%   53.87%   +0.60%     
- Complexity      651      834     +183     
============================================
  Files           208      224      +16     
  Lines         14303    14734     +431     
  Branches       5845     5600     -245     
============================================
+ Hits           7619     7938     +319     
- Misses         6308     6390      +82     
- Partials        376      406      +30     

Flag	Coverage Δ
java	62.01% <76.42%> (+0.33%)	⬆️

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[qianye1001]

Review Suggestions

1. Per-group buffering for FIFO mode — The current batch buffer is global across all message groups. In FIFO mode, a batch may contain messages from different groups, and a failure sends all to DLQ together. Consider whether per-group buffering would provide stricter FIFO guarantees.

2. directExecutor() in submitBatch() callback — handleResult() runs on the same thread that completes the future. If ack/nack does blocking I/O, it could delay other callbacks. Consider using the consumption executor instead of MoreExecutors.directExecutor().

3. Add FifoBatchConsumeServiceTest — BatchConsumeService, BatchConsumeTask, and BatchPolicy all have tests, but FifoBatchConsumeService lacks dedicated coverage for FIFO ordering, retry, and DLQ scenarios.

4. Constructor backward compat — The old 7-param convenience constructor in PushConsumerImpl was removed. Consider keeping it as a deprecated overload, or call this out in release notes.