feat: Add Basic Prefix Sum Algorithm with Tests. FIXES #1783

[Anshusinghh]

What does this PR do?

This PR adds an implementation of the Prefix Sum algorithm (in-place cumulative sum) in JavaScript.

Details

• Implements prefixSum in Prefix-Sum/BasicPrefixSum.js
  • Validates input (must be numeric array).
  • Throws TypeError on invalid inputs.
  • Modifies the array in-place and returns the same reference.
• Adds Prefix-Sum/BasicPrefixSum.test.js with unit tests using Vitest.
  • Covers integers, negatives, floats, empty input, and error handling.

Why is this needed?

Prefix sum is a fundamental algorithm widely used in competitive programming and data processing. Having an in-place implementation ensures O(1) extra space.

Checklist

• Code follows repository style guidelines
• Added tests with Vitest
• npm test passes locally
• No console statements

---

Thanks for reviewing 🙏 Please let me know if changes are needed.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.93%. Comparing base (08d8c6b) to head (0b727bf).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1797      +/-   ##
==========================================
+ Coverage   85.91%   85.93%   +0.01%     
==========================================
  Files         379      380       +1     
  Lines       19778    19800      +22     
  Branches     3015     3023       +8     
==========================================
+ Hits        16993    17015      +22     
  Misses       2785     2785              

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