move utils into internal package

[JacksonTian]

You need to complete

• unit tests and/or feature tests
• documentation is changed or added

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.85%. Comparing base (e6ece0c) to head (025af96).

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #92   +/-   ##
=======================================
  Coverage   99.84%   99.85%           
=======================================
  Files          21       22    +1     
  Lines        1280     1358   +78     
=======================================
+ Hits         1278     1356   +78     
  Partials        2        2           

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