refactor: Anagrams

[alxkm]

Class cleanup.
Readability improvements.
Tests refactor.

• 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 91.17647% with 3 lines in your changes missing coverage. Please review.

Project coverage is 47.65%. Comparing base (7e9cdad) to head (38e47b3).

Files	Patch %	Lines
.../main/java/com/thealgorithms/strings/Anagrams.java	91.17%	0 Missing and 3 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5390      +/-   ##
============================================
+ Coverage     47.60%   47.65%   +0.04%     
- Complexity     2944     2948       +4     
============================================
  Files           524      524              
  Lines         15312    15298      -14     
  Branches       2906     2906              
============================================
  Hits           7290     7290              
+ Misses         7720     7708      -12     
+ Partials        302      300       -2     

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