Add scripts/sum.js with sum function and assert tests

[devin-ai-integration]

Summary

Adds scripts/sum.js — a small JavaScript program that:

• Defines a sum(a, b) function returning a + b
• Prints sum(2, 3) to the console
• Includes assert-based tests verifying correctness

Review & Testing Checklist for Human

• Run node scripts/sum.js and confirm output is 5 followed by All tests passed

Notes

Self-contained utility script with no external dependencies.

Link to Devin session: https://localstack.devinenterprise.com/sessions/79aeee49da1b46f08a4d932d051cb8e7

[devin-ai-integration]

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