Refactor BCD Conversion docs and add more tests

[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

Attention: Patch coverage is 92.30769% with 1 line in your changes missing coverage. Please review.

Project coverage is 64.11%. Comparing base (bae7f89) to head (60a7169).

Files with missing lines	Patch %	Lines
...m/thealgorithms/bitmanipulation/BcdConversion.java	92.30%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5762      +/-   ##
============================================
+ Coverage     64.10%   64.11%   +0.01%     
- Complexity     4195     4199       +4     
============================================
  Files           586      586              
  Lines         16372    16376       +4     
  Branches       3158     3159       +1     
============================================
+ Hits          10495    10500       +5     
  Misses         5448     5448              
+ Partials        429      428       -1     

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