fix: fix prefix lookup in basickv and add corresponding test

[SYaoJun]

What's changed and how does it work?

1. add prefixlookup based on pessimistic iterator
2. add test for prefixlookup BasicKV::PrefixLookup: I notice the founction may return one KV pair. it is designing for that or a bug? #133

[codecov]

Codecov Report

Attention: Patch coverage is 88.88889% with 2 lines in your changes missing coverage. Please review.

Project coverage is 62.29%. Comparing base (a19fa4f) to head (addeac5).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/btree/BasicKV.cpp	88.88%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #134      +/-   ##
==========================================
+ Coverage   62.23%   62.29%   +0.06%     
==========================================
  Files          84       84              
  Lines        6421     6418       -3     
  Branches     3001     2953      -48     
==========================================
+ Hits         3996     3998       +2     
+ Misses       2074     2060      -14     
- Partials      351      360       +9     

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[zz-jason]

LGTM