Test cases project euler 9 (#1571)

* 📦 NEW: Added solution for ProjectEuler-007

* 🐛 FIX: Spelling mistake fixes

* 👌 IMPROVE: changed variable name from `inc` to `candidateValue` and thrown error in case of invalid input

* 👌 IMPROVE: Modified the code

* 👌 IMPROVE: Added test case for ProjectEuler Problem001

* 👌 IMPROVE: Added test cases for Project Euler Problem 4

* 👌 IMPROVE: auto prettier fixes

* 👌 IMPROVE: Added test cases for project euler problem 9

* Updated Documentation in README.md

* Updated Documentation in README.md

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Co-authored-by: Omkarnath Parida <omkarnath.parida@yocket.in>
Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>