prettier fixes & added test cases for Project Euler problem 4 (#1566)

* 📦 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

---------

Co-authored-by: Omkarnath Parida <omkarnath.parida@yocket.in>

Project-Euler/test/Problem004.test.js

@@ -0,0 +1,11 @@
+import { largestPalindromic } from '../Problem004.js'
+
+describe('Largest Palindromic Number', () => {
+  test('if digit is 2', () => {
+    expect(largestPalindromic(2)).toBe(9009)
+  })
+  // Project Euler Condition Check
+  test('if digit is 3', () => {
+    expect(largestPalindromic(3)).toBe(906609)
+  })
+})