Forward taylor expansion keyword arguments to internal substitutions

[hersle]

Fixes the added test.

taylor() calls substitute() internally, which uses fold=true by defaults, which evaluates numerical expressions, which may not always be desired. These changes allow passing fold=true to prevent it.

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 0% with 12 lines in your changes missing coverage. Please review.

Project coverage is 8.88%. Comparing base (eced900) to head (9a5651c).
Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
src/taylor.jl	0.00%	12 Missing ⚠️

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Additional details and impacted files

@@          Coverage Diff           @@
##           master   #1429   +/-   ##
======================================
  Coverage    8.88%   8.88%           
======================================
  Files          51      51           
  Lines        4876    4876           
======================================
  Hits          433     433           
  Misses       4443    4443           

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