feat: change pointer to struct

[suzuki-shunsuke]

BREAKING CHANGE: the signature is changed

[codecov-commenter]

Codecov Report

Merging #23 into master will increase coverage by 1.46%.
The diff coverage is 75.00%.

@@            Coverage Diff             @@
##           master      #23      +/-   ##
==========================================
+ Coverage   62.06%   63.52%   +1.46%     
==========================================
  Files           1        1              
  Lines          87       85       -2     
==========================================
  Hits           54       54              
+ Misses         24       23       -1     
+ Partials        9        8       -1     

Impacted Files	Coverage Δ
httpclient/client.go	63.52% <75.00%> (+1.46%)	⬆️

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