Add Junit tests for ColumnarTranspositionCipher.java

[Hardvan]

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized it.
• All filenames are in PascalCase.
• All functions and variable names follow Java naming conventions.
• All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.
• All new code is formatted with clang-format -i --style=file path/to/your/file.java

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 57.46%. Comparing base (f80850b) to head (cb2487a).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5599      +/-   ##
============================================
+ Coverage     57.07%   57.46%   +0.38%     
- Complexity     3615     3639      +24     
============================================
  Files           545      545              
  Lines         15722    15708      -14     
  Branches       2995     2994       -1     
============================================
+ Hits           8974     9026      +52     
+ Misses         6369     6301      -68     
- Partials        379      381       +2     

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[siriak]

Looks good, thanks!

[Hardvan]

Thanks!