Addition of RandomString

[ronanstokes-db]

Proposed changes

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• Bug fix (non-breaking change which fixes an issue)
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• Breaking change (fix or feature that would cause existing functionality to not work as expected)
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Checklist

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• Lint and unit tests pass locally with my changes
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[codecov]

Codecov Report

Attention: 63 lines in your changes are missing coverage. Please review.

Comparison is base (250f92a) 91.97% compared to head (0e84261) 90.34%.
Report is 8 commits behind head on master.

Files	Patch %	Lines
dbldatagen/value_based_prng.py	68.90%	35 Missing and 2 partials ⚠️
dbldatagen/text_generatestring.py	65.33%	23 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #183      +/-   ##
==========================================
- Coverage   91.97%   90.34%   -1.64%     
==========================================
  Files          23       25       +2     
  Lines        2680     2879     +199     
  Branches      452      483      +31     
==========================================
+ Hits         2465     2601     +136     
- Misses        128      186      +58     
- Partials       87       92       +5     

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[CLAassistant]

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