[fix][test] Fix flaky ConsumedLedgersTrimTest.testAdminTrimLedgers

[merlimat]

Flaky test failure

org.awaitility.core.ConditionTimeoutException: Assertion condition expected [1] but found [2] within 10 seconds.
	at org.apache.pulsar.broker.service.ConsumedLedgersTrimTest.testAdminTrimLedgers

Also reproduces as producer timeout when running with invocationCount>1.

Summary

Follow-up to #25342. Three issues causing flakiness:

1. Fixed producer name "producer-name" causes 30s timeout when running with invocationCount>1 because the previous invocation's partitioned producer (3 sub-producers) may not have fully disconnected yet, and the new producer with the same name waits for the old one.

   • Fix: remove the fixed producerName so each invocation gets a unique auto-generated name.

2. Assertion too strict — expects exactly 1 ledger after trim, but with maxEntriesPerLedger=2, if partition-0 receives an even number of messages, the last ledger is full and a new empty active ledger is created. After trimming, 2 ledgers remain.

   • Fix: assert <= 2 instead of == 1.

3. Trim is async — admin.topics().trimTopic() returns immediately but the actual ledger deletion happens in the background. The mark-delete position may not be persisted yet when the first trim runs.

   • Fix: re-trigger trimConsumedLedgersInBackground() inside the Awaitility loop.

Documentation

• doc-not-needed
  (Your PR doesn't need any doc update)

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.75%. Comparing base (74f4e5a) to head (c62dd52).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #25360      +/-   ##
============================================
+ Coverage     72.73%   72.75%   +0.02%     
+ Complexity    34264    33876     -388     
============================================
  Files          1954     1954              
  Lines        154792   154792              
  Branches      17731    17731              
============================================
+ Hits         112586   112622      +36     
+ Misses        33170    33157      -13     
+ Partials       9036     9013      -23     

Flag	Coverage Δ
inttests	25.72% <ø> (-0.19%)	⬇️
systests	22.56% <ø> (+0.08%)	⬆️
unittests	73.73% <ø> (+<0.01%)	⬆️

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