Feat: Add FourSumProblem and JUnit Test

[SAIVARDHAN15]

• 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 92.30769% with 2 lines in your changes missing coverage. Please review.

Project coverage is 64.26%. Comparing base (213fd5a) to head (286e49b).

Files with missing lines	Patch %	Lines
...in/java/com/thealgorithms/misc/FourSumProblem.java	92.30%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5798      +/-   ##
============================================
+ Coverage     64.21%   64.26%   +0.05%     
- Complexity     4216     4230      +14     
============================================
  Files           588      589       +1     
  Lines         16426    16452      +26     
  Branches       3170     3180      +10     
============================================
+ Hits          10548    10573      +25     
- Misses         5448     5449       +1     
  Partials        430      430              

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