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