pointer type changes + replace if with switch

[badasahog]

the char* was always casted to another type anyway, and void* denotes this pattern better.

[github-actions]

• HEAD=char2void slower P<0.001 for fwrite refactored in #6393
  

Generated via commit b99ae81

Download link for the artifact containing the test results: ↓ atime-results.zip

Task	Duration
R setup and installing dependencies	5 minutes and 10 seconds
Installing different package versions	10 minutes and 27 seconds
Running and plotting the test cases	2 minutes and 43 seconds

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.09%. Comparing base (88635ad) to head (b99ae81).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7247   +/-   ##
=======================================
  Coverage   99.09%   99.09%           
=======================================
  Files          83       83           
  Lines       16089    16095    +6     
=======================================
+ Hits        15944    15950    +6     
  Misses        145      145           

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