feat: add Difference Array algorithm implementation and tests

[singhc7]

Description

This PR adds the Difference Array algorithm implementation to the existing prefixsum package.

The Difference Array is an auxiliary data structure that enables efficient range update operations. Unlike a standard array where updating a range $[L, R]$ takes $O(N)$ time, the Difference Array allows for range updates in $O(1)$ time complexity, with the final array reconstruction taking $O(N)$.

Key Features of Implementation:

• Optimized Performance: Implements a branchless update method for constant-time operations.
• Overflow Safety: Uses long[] internally to prevent integer overflow during intermediate range updates.
• Comprehensive Testing: Includes a dedicated test class (DifferenceArrayTest.java) covering standard cases, edge cases (single element, full range), and stress tests (boundary conditions).
• Documentation: Includes Javadoc with complexity analysis and a reference to Wikipedia as per contribution guidelines.

Checklist

• 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 algorithms include a corresponding test class that validates their functionality.
• 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.
✅ Project coverage is 79.11%. Comparing base (2ea3873) to head (e83eb74).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #7244      +/-   ##
============================================
+ Coverage     79.09%   79.11%   +0.01%     
- Complexity     6974     6985      +11     
============================================
  Files           783      784       +1     
  Lines         22950    22971      +21     
  Branches       4512     4515       +3     
============================================
+ Hits          18152    18173      +21     
  Misses         4077     4077              
  Partials        721      721              

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[alxkm]

Looks good. Thank you for the contribution.