Add keyword argument for contract operators, clean simulation pipeline

[lukem12345]

Currently, when compiling a Decapode, certain chains of matrix operations are pre-multiplied into single matrices. This cuts down on the number of matrix-vector multiplications in generated simulation code.

However the pre-multiplication of matrix operators can cause issues for certain autodiff implementations.

So, this PR adds a keyword argument to gensim that controls this behavior.

[codecov]

Codecov Report

Attention: Patch coverage is 91.37931% with 5 lines in your changes missing coverage. Please review.

Project coverage is 67.69%. Comparing base (cc035d8) to head (6d7ad46).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/simulation.jl	91.37%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #287      +/-   ##
==========================================
- Coverage   69.00%   67.69%   -1.32%     
==========================================
  Files           5        5              
  Lines         655      616      -39     
==========================================
- Hits          452      417      -35     
+ Misses        203      199       -4     

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