feat: Add Prefix Sum category with 1D and 2D implementations

[singhc7]

Fixes #7209

This PR introduces a new package prefixsum as requested, providing a robust foundation for prefix-based algorithms.

Changes:

1. PrefixSum.java (1D): Implements standard prefix sum for efficient range queries ($O(1)$).
2. PrefixSum2D.java: Implements 2D prefix sum for efficient sub-matrix sum queries using the inclusion-exclusion principle.

Key Features:

• Overflow Protection: Both implementations internally use long[] to store sums, preventing integer overflow when the sum of elements exceeds Integer.MAX_VALUE.
• Comprehensive Testing: Added JUnit 5 tests covering:
  • Basic range queries.
  • Edge cases (single element, empty arrays, mixed signs).
  • Boundary checks (invalid indices, rectangular matrices).
  • Large number overflow scenarios.

• 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 79.08%. Comparing base (1b9373e) to head (c92da2d).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #7220      +/-   ##
============================================
+ Coverage     79.06%   79.08%   +0.02%     
- Complexity     6951     6971      +20     
============================================
  Files           780      782       +2     
  Lines         22921    22947      +26     
  Branches       4506     4512       +6     
============================================
+ Hits          18122    18148      +26     
  Misses         4077     4077              
  Partials        722      722              

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