Keep processing a batch when one queued item throws

[LI123456mo]

Fixes #16469

What is the purpose of the change

When handling one item of a batch threw inside BatchExecutorQueue, the rest of the batch had already been taken off the queue and was silently dropped. TripleWriteQueue only handled CompletionException, so any other failure left the failing command's promise pending, and a failing last command skipped the channel flush for the earlier writes in the same batch.

Brief changelog

• BatchExecutorQueue: failures in prepare and flush are caught and logged per item, so the remaining items of the batch are still handled. If the executor rejects the task that drains the queue, the scheduled flag is reset so a later enqueue schedules processing again.
• TripleWriteQueue: any failure completes only that command's promise as failed, and the channel is flushed even when the last command of the batch fails.

Verifying this change

Added BatchExecutorQueueTest and TripleWriteQueueTest covering failures in the middle, at the end, at a chunk boundary and multiple failures in one batch, executor rejection, promise completion, and flushing after a failing last command.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 96.29630% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 60.93%. Comparing base (df9c5e1) to head (b5a8de9).

Files with missing lines	Patch %	Lines
...o/rpc/protocol/tri/transport/TripleWriteQueue.java	87.50%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                3.3   #16470      +/-   ##
============================================
+ Coverage     60.91%   60.93%   +0.01%     
- Complexity    11769    11778       +9     
============================================
  Files          1953     1953              
  Lines         89275    89292      +17     
  Branches      13474    13474              
============================================
+ Hits          54382    54409      +27     
+ Misses        29312    29302      -10     
  Partials       5581     5581              

Flag	Coverage Δ
integration-tests-java21	32.08% <44.44%> (-0.06%)	⬇️
integration-tests-java8	32.21% <44.44%> (+<0.01%)	⬆️
samples-tests-java21	32.18% <44.44%> (-0.01%)	⬇️
samples-tests-java8	29.82% <44.44%> (+0.01%)	⬆️
unit-tests-java11	59.20% <96.29%> (+0.02%)	⬆️
unit-tests-java17	58.66% <96.29%> (+0.01%)	⬆️
unit-tests-java21	58.66% <96.29%> (-0.03%)	⬇️
unit-tests-java25	58.64% <96.29%> (+0.03%)	⬆️
unit-tests-java8	59.22% <96.29%> (+0.04%)	⬆️

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