refactor: DuplicateBrackets

[alxkm]

Class cleanup.
Readability improvements.
Added tests.

• 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 72.72727% with 3 lines in your changes missing coverage. Please review.

Project coverage is 50.72%. Comparing base (e2aaefe) to head (e73330d).

Files with missing lines	Patch %	Lines
...va/com/thealgorithms/stacks/DuplicateBrackets.java	72.72%	0 Missing and 3 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5424      +/-   ##
============================================
+ Coverage     50.65%   50.72%   +0.06%     
- Complexity     3131     3136       +5     
============================================
  Files           523      523              
  Lines         15125    15128       +3     
  Branches       2879     2880       +1     
============================================
+ Hits           7662     7674      +12     
+ Misses         7141     7129      -12     
- Partials        322      325       +3     

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[BamaCharanChhandogi]

Thank you for your contribution to the DuplicateBrackets class. Your changes have improved the code's readability and robustness. To further enhance the functionality and versatility of this class, we suggest the following updates:

[alxkm]

@BamaCharanChhandogi, thank you. But which updates you would suggest?

[BamaCharanChhandogi]

LGTM