feat: Add Basic Prefix Sum Algorithm with Tests (Fixes #1783)

[Anshusinghh]

FIXES #1783

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.