refine index_kv constructor

[JacksonYao287]

this PR refines index_kv constructor, which will not do reinterpret_cast to bypass the issue in #403

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 52.76%. Comparing base (1746bcc) to head (fd10f0f).
⚠️ Report is 168 commits behind head on main.
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Additional details and impacted files

@@             Coverage Diff             @@
##             main     #404       +/-   ##
===========================================
- Coverage   63.15%   52.76%   -10.40%     
===========================================
  Files          32       36        +4     
  Lines        1900     5276     +3376     
  Branches      204      658      +454     
===========================================
+ Hits         1200     2784     +1584     
- Misses        600     2199     +1599     
- Partials      100      293      +193     

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