fix(sei-db): fix flaky RocksDB parallel iteration test

[pdrobnjak]

Summary

• Fixes a use-after-free race condition in the RocksDB iterator that caused TestDatabaseParallelIterationVersions to flake
• The ReadOptions object (and its timestamp slice) created by newTSReadOptions() was passed to NewIteratorCF() but never stored, making it eligible for GC while the C++ iterator still held a dangling Slice pointer to the timestamp data
• Under parallel access (99 goroutines in the test), GC pressure caused iterators to read with corrupted timestamps, returning values from wrong versions (e.g., expected val002-011 but got val002-017)
• The fix stores ReadOptions in the iterator struct and calls Destroy() on Close(), ensuring the timestamp data remains valid for the iterator's lifetime
• Also fixes the same ReadOptions leak in getSlice() (used by Get/Has)

Test plan

• TestDatabaseParallelIterationVersions — the previously flaky test should now pass consistently
• All other RocksDB tests unaffected (no API changes beyond the internal plumbing)

🤖 Generated with Claude Code

[github-actions]

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Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Feb 27, 2026, 2:22 PM

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 57.65%. Comparing base (83c9561) to head (c91e04b).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2928      +/-   ##
==========================================
- Coverage   58.12%   57.65%   -0.48%     
==========================================
  Files        2111     2111              
  Lines      173544   173671     +127     
==========================================
- Hits       100879   100130     -749     
- Misses      63706    64586     +880     
+ Partials     8959     8955       -4     

Flag	Coverage Δ
sei-db	69.72% <ø> (+0.21%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
sei-db/db_engine/rocksdb/mvcc/db.go	58.80% <ø> (+0.39%)	⬆️

... and 78 files with indirect coverage changes

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