refactor(sei-db): return cleanup closure from newTSReadOptions

[pdrobnjak]

Stacked on #2928.

Summary

• Pushes ReadOptions creation into the iterator constructors so callers never handle ReadOptions directly — eliminates the possibility of forgetting to Destroy() them
• newIterator() creates a versioned iterator with internally managed ReadOptions, used by Iterator() and ReverseIterator()
• newRangeIterator() creates a timestamp-range iterator with internally managed ReadOptions, used by RawIterate()
• newTSReadOptions() now returns a cleanup closure alongside the ReadOptions — for non-iterator uses (getSlice), the compiler forces you to either use or explicitly discard the second return value
• The iterator stores a cleanup func() instead of *ReadOptions, called on Close()

Test plan

• No behavioral changes — purely structural refactor
• All RocksDB tests should pass (same constructors, same lifecycle, just encapsulated)

🤖 Generated with Claude Code

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Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Feb 19, 2026, 10:14 AM

[codecov]

Codecov Report

❌ Patch coverage is 96.55172% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 57.34%. Comparing base (8f3bc86) to head (73de9e4).

Files with missing lines	Patch %	Lines
sei-db/db_engine/rocksdb/mvcc/db.go	88.88%	1 Missing ⚠️

Additional details and impacted files

@@                   Coverage Diff                    @@
##           pd/fix-rocks-db-ci-fail    #2929   +/-   ##
========================================================
  Coverage                    57.34%   57.34%           
========================================================
  Files                         2095     2095           
  Lines                       172896   172896           
========================================================
+ Hits                         99142    99145    +3     
- Misses                       64867    64868    +1     
+ Partials                      8887     8883    -4     

Flag	Coverage Δ
sei-chain	52.84% <ø> (+<0.01%)	⬆️
sei-cosmos	48.19% <ø> (ø)
sei-db	69.18% <96.55%> (ø)

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/iterator.go	86.31% <100.00%> (ø)
sei-db/db_engine/rocksdb/mvcc/db.go	58.23% <88.88%> (ø)

... and 29 files with indirect coverage changes

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