refactor: Enhance docs, remove `main`. add more tests in `HexaDecimal…

[Hardvan]

…ToBinary`

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

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 72.11%. Comparing base (cfa35a4) to head (23f13df).

Files with missing lines	Patch %	Lines
...thealgorithms/conversions/HexaDecimalToBinary.java	0.00%	2 Missing :warning:

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5922      +/-   ##
============================================
- Coverage     72.13%   72.11%   -0.02%     
+ Complexity     4947     4943       -4     
============================================
  Files           650      650              
  Lines         17560    17555       -5     
  Branches       3385     3384       -1     
============================================
- Hits          12667    12660       -7     
- Misses         4414     4416       +2     
  Partials        479      479              

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