add a few error hints for factorizations on exotic number types

[baggepinnen]

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[JuliaControlBot]

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.28%. Comparing base (aa299b7) to head (e2dea34).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
lib/ControlSystemsBase/src/ControlSystemsBase.jl	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1016      +/-   ##
==========================================
- Coverage   92.35%   92.28%   -0.08%     
==========================================
  Files          41       41              
  Lines        5155     5159       +4     
==========================================
  Hits         4761     4761              
- Misses        394      398       +4     

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