[ISSUE #10912] Fix native memory leak in PopConsumerRocksdbStore

[majialoong]

Which Issue(s) This PR Fixes

• Fixes [Bug] PopConsumerRocksdbStore leaks RocksDB Slice objects #10912

Brief Description

Close the RocksDB Slice objects created in scanExpiredRecords() to prevent native memory leaks.

How Did You Test This Change?

Ran the existing PopConsumerRocksdbStoreTest and verified that native memory remains stable during repeated scans.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 48.35%. Comparing base (97a7975) to head (b2f2cd7).

Additional details and impacted files

@@              Coverage Diff              @@
##             develop   #10913      +/-   ##
=============================================
- Coverage      48.46%   48.35%   -0.12%     
+ Complexity     13584    13553      -31     
=============================================
  Files           1380     1380              
  Lines         101195   101197       +2     
  Branches       13130    13130              
=============================================
- Hits           49040    48929     -111     
- Misses         46188    46279      +91     
- Partials        5967     5989      +22     

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[RockteMQ-AI]

Summary

This PR fixes a native memory leak in PopConsumerRocksdbStore.scanExpiredRecords() by properly closing RocksDB Slice objects in a try-with-resources block.

The fix is correct — Slice objects hold native (off-heap) memory via RocksDB's C++ layer and must be explicitly closed. Previously, they were created inline inside ReadOptions and never released, causing a native memory leak under sustained pop-consume traffic.

LGTM. Clean, minimal fix.

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