feat: add kv client

[LingKa28]

Base on #2

Please briefly answer these questions:

• what problem are you trying to solve? (or if there's no problem, what's the motivation for this change?)
  Add KV clinet

• what changes does this pull request make?

  • add kv client

• are there any non-obvious implications of these changes? (does it break compatibility with previous versions, etc)
  No.

[codecov]

Codecov Report

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (42e35cd) 79.24% compared to head (92420d0) 93.97%.

Files	Patch %	Lines
client/kv.py	90.16%	4 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main       #6       +/-   ##
===========================================
+ Coverage   79.24%   93.97%   +14.73%     
===========================================
  Files           4        8        +4     
  Lines         159      382      +223     
  Branches       20       23        +3     
===========================================
+ Hits          126      359      +233     
+ Misses         24       16        -8     
+ Partials        9        7        -2     

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