perf(goleveldb): use LevelDB Has to skip value reads

[songgaoye]

Replace Get() call with native LevelDB Has() method to check key existence without reading the value data.
This reduces I/O and memory overhead for Has() operations.

the same cosmos/cosmos-db#145

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PR checklist

• Tests written/updated
• Changelog entry added in .changelog (we use unclog to manage our changelog)

[greptile-apps]

PR author is not in the allowed authors list.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.37%. Comparing base (fb4f703) to head (a682ce8).
⚠️ Report is 78 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #288      +/-   ##
==========================================
+ Coverage   76.80%   79.37%   +2.56%     
==========================================
  Files          23       23              
  Lines        2048     1697     -351     
==========================================
- Hits         1573     1347     -226     
+ Misses        403      280     -123     
+ Partials       72       70       -2     

Files with missing lines	Coverage Δ
goleveldb.go	63.46% <100.00%> (+3.61%)	⬆️

... and 21 files with indirect coverage changes

Files with missing lines	Coverage Δ
goleveldb.go	63.46% <100.00%> (+3.61%)	⬆️

... and 21 files with indirect coverage changes

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