Clean up herk_wrapper! and add 5-arg tests

[dkarrasch]

This method can only be reached with complex eltypes, and after promotion of alpha and beta, they cannot be Bool anymore. Also, this adds 5-arg mul! of which I'm not sure we had some (even though coverage said it was covered, which is strange because it shouldn't due to the issue fixed in #1247).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.99%. Comparing base (e64a3df) to head (39588e0).
Report is 34 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1254   +/-   ##
=======================================
  Coverage   91.99%   91.99%           
=======================================
  Files          34       34           
  Lines       15459    15460    +1     
=======================================
+ Hits        14221    14222    +1     
  Misses       1238     1238           

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