Added benchmark score for PrivalFromString (#378)

[kirubaspace]

This adds benchmark testing for PrivalFromString. This is intended to compare benchmarking score for reference in the future if further optimisations/changes done in the corresponding function.

Make sure that your pull request follows the guidelines specified in the
Guidelines for Contributing.

[goatshriek]

Thanks very much for putting this together! I've included a few comments for you to address, after which I will run the CI tests.

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (c54a498) 91.69% compared to head (ba4615f) 91.78%.
Report is 3 commits behind head on latest.

Additional details and impacted files

@@            Coverage Diff             @@
##           latest     #379      +/-   ##
==========================================
+ Coverage   91.69%   91.78%   +0.09%     
==========================================
  Files          44       44              
  Lines        3743     3772      +29     
  Branches      489      497       +8     
==========================================
+ Hits         3432     3462      +30     
  Misses        216      216              
+ Partials       95       94       -1     

see 4 files with indirect coverage changes

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[goatshriek]

Everything looks good now! The final thing for you to correct is simply add an include for <string> to priority.cpp (due to the usage of std::string), which should satisfy the include check in the Static Analysis workflow.