[Feature] add random_state to complexity_symbolize

[danibene]

Description

This PR aims to allow for setting the random seed in complexity_symbolize(). See also #879

Proposed Changes

I added a random_state argument to the complexity_symbolize() function so that the seed is passed to scipy.cluster.vq.kmeans2()

Checklist

• I have read the CONTRIBUTING file.
• My PR is targetted at the dev branch (and not towards the master branch).

[codecov-commenter]

Codecov Report

Patch coverage: 75.00% and project coverage change: +0.01% 🎉

Comparison is base (a802b57) 55.23% compared to head (22323a7) 55.25%.
Report is 3 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #881      +/-   ##
==========================================
+ Coverage   55.23%   55.25%   +0.01%     
==========================================
  Files         297      297              
  Lines       13917    13918       +1     
==========================================
+ Hits         7687     7690       +3     
+ Misses       6230     6228       -2     

Files Changed	Coverage Δ
neurokit2/complexity/utils_complexity_symbolize.py	20.90% <75.00%> (+1.46%)	⬆️

... and 4 files with indirect coverage changes

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