Support hermitian types for KernelMatrix

[maltezfaria]

Fixes #80

[codecov]

Codecov Report

Attention: Patch coverage is 61.53846% with 5 lines in your changes missing coverage. Please review.

Project coverage is 77.18%. Comparing base (82eed5b) to head (4a1d592).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/multiplication.jl	54.54%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #81      +/-   ##
==========================================
+ Coverage   75.18%   77.18%   +1.99%     
==========================================
  Files          14       14              
  Lines        1475     1477       +2     
==========================================
+ Hits         1109     1140      +31     
+ Misses        366      337      -29     

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