Add recursive factorial implementation with tests

[koushik-sai]

• Added a recursive implementation of factorial in the recursion package
• Followed utility-class pattern used across the repository
• Included JUnit tests for base cases, positive input, and negative input

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.89%. Comparing base (48e02b3) to head (0bc3398).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #7178      +/-   ##
============================================
- Coverage     78.90%   78.89%   -0.01%     
- Complexity     6858     6862       +4     
============================================
  Files           771      772       +1     
  Lines         22688    22697       +9     
  Branches       4457     4459       +2     
============================================
+ Hits          17901    17906       +5     
- Misses         4072     4073       +1     
- Partials        715      718       +3     

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[DenizAltunkapan]

there already exists a recursive implementation @koushik-sai https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/maths/FactorialRecursion.java .
Would you suggest moving the existing class into the recursive package?
If so, please move it there and remove your implementation.

[koushik-sai]

Thanks for the suggestion 👍
I’ve moved the existing FactorialRecursion from the maths package to the recursion package, removed the duplicate implementation introduced in this PR, updated the corresponding tests, and applied clang-format. All tests pass locally.