refactor: Enhance docs, add more tests in `LRUCache`

[Hardvan]

• [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

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 67.39%. Comparing base (520e464) to head (0724f4f).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5950      +/-   ##
============================================
+ Coverage     67.32%   67.39%   +0.06%     
- Complexity     4571     4575       +4     
============================================
  Files           620      620              
  Lines         17147    17147              
  Branches       3312     3312              
============================================
+ Hits          11545    11557      +12     
+ Misses         5149     5142       -7     
+ Partials        453      448       -5     

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