mock REST API calls in tests

[2bndy5]

resolves #18
resolves #11

[codecov]

Codecov Report

Attention: Patch coverage is 93.89920% with 23 lines in your changes missing coverage. Please review.

Project coverage is 97.28%. Comparing base (11ead4e) to head (8d2593d).
Report is 2 commits behind head on main.

Files	Patch %	Lines
cpp-linter-lib/src/rest_api/github_api.rs	95.07%	10 Missing ⚠️
cpp-linter-lib/src/rest_api/mod.rs	93.79%	8 Missing ⚠️
cpp-linter-lib/src/clang_tools/clang_tidy.rs	82.75%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #21      +/-   ##
==========================================
+ Coverage   87.66%   97.28%   +9.61%     
==========================================
  Files          12       13       +1     
  Lines        2230     2431     +201     
==========================================
+ Hits         1955     2365     +410     
+ Misses        275       66     -209     

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