General: Add nodiscard attribute to create* API

[stotko]

The create* API returns the newly constructed and initialized object that can then be used. However, ignoring the return value will result in loosing access to that object and thus will lead not only to a likely crash but also to a memory leak. Add the [[nodiscard]] attribute to these functions to better warn users of this issue and indicate the correct usage of these functions.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.33%. Comparing base (1f0b2d5) to head (64574c9).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #409   +/-   ##
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  Coverage   97.33%   97.33%           
=======================================
  Files          31       31           
  Lines        2512     2512           
=======================================
  Hits         2445     2445           
  Misses         67       67           

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