feat: Test running overhaul, switch to Prettier & reformat everything (#1407)

* chore: Switch to Node 20 + Vitest

* chore: migrate to vitest mock functions

* chore: code style (switch to prettier)

* test: re-enable long-running test

Seems the switch to Node 20 and Vitest has vastly improved the code's and / or the test's runtime!

see #1193

* chore: code style

* chore: fix failing tests

* Updated Documentation in README.md

* Update contribution guidelines to state usage of Prettier

* fix: set prettier printWidth back to 80

* chore: apply updated code style automatically

* fix: set prettier line endings to lf again

* chore: apply updated code style automatically

---------

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
Co-authored-by: Lars Müller <34514239+appgurueu@users.noreply.github.com>

Data-Structures/Array/test/Reverse.test.js

@@ -1,13 +1,14 @@
 import { Reverse } from '../Reverse.js'
-import each from 'jest-each'
 
 describe('reverse elements in an array', () => {
-  each`
-  array | expected
-  ${[]} | ${[]}
-  ${[1]} | ${[1]}
-  ${[1, 2, 3, 4]} | ${[4, 3, 2, 1]}
-  `.test('returns $expected when given $array', ({ array, expected }) => {
-      expect(Reverse(array)).toEqual(expected)
-    })
+  it.each([
+    [[], []],
+    [[1], [1]],
+    [
+      [1, 2, 3, 4],
+      [4, 3, 2, 1]
+    ]
+  ])('returns %j when given %j', (array, expected) => {
+    expect(Reverse(array)).toEqual(expected)
+  })
 })