restructuring: create a lib and a binary using that lib

[vanilla-extracts]

Implements #90

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 60.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 11.17%. Comparing base (9c93ed4) to head (d5d95f2).

Files with missing lines	Patch %	Lines
crates/mini-calc/src/main.rs	0.00%	2 Missing ⚠️
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Additional details and impacted files

@@             Coverage Diff              @@
##           mistress      #91      +/-   ##
============================================
+ Coverage     11.11%   11.17%   +0.05%     
============================================
  Files            23       23              
  Lines          4677     4680       +3     
============================================
+ Hits            520      523       +3     
  Misses         4157     4157              

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