refactor: Enhance docs, add more tests in Bag

[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 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 67.30%. Comparing base (fef1f3c) to head (1765e72).

Files with missing lines	Patch %	Lines
...ava/com/thealgorithms/datastructures/bags/Bag.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5947      +/-   ##
============================================
+ Coverage     67.29%   67.30%   +0.01%     
  Complexity     4568     4568              
============================================
  Files           620      620              
  Lines         17143    17143              
  Branches       3310     3310              
============================================
+ Hits          11536    11538       +2     
+ Misses         5153     5152       -1     
+ Partials        454      453       -1     

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