[ISSUE # 10086] Fix timer engine switch to persist correct config key

[Liu-ZhenYu]

Motivation
switchTimerEngine writes timerUseRocksDB to the broker configuration, but the actual config key is timerRocksDBEnable. As a result, the switch isn’t persisted and may revert after restart.There’s also a typo in the error message.

Changes

• Persist timerRocksDBEnable instead of timerUseRocksDB
• Fix typo in error message (muse → must) and reference correct key name

Impact
Ensures engine switch is persisted correctly and improves user-facing guidance.

Test Plan

• Manual: switch to RocksDB engine, verify timerRocksDBEnable=true is written to config; restart broker and confirm RocksDB engine remains enabled.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 48.86%. Comparing base (ec7db8d) to head (56de824).

Files with missing lines	Patch %	Lines
...ocketmq/broker/processor/AdminBrokerProcessor.java	0.00%	2 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             develop   #10085      +/-   ##
=============================================
- Coverage      48.91%   48.86%   -0.06%     
+ Complexity     13364    13351      -13     
=============================================
  Files           1373     1373              
  Lines          99868    99868              
  Branches       12903    12903              
=============================================
- Hits           48855    48798      -57     
- Misses         45097    45148      +51     
- Partials        5916     5922       +6     

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