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>

String/test/PermutateString.test.js

@@ -2,7 +2,9 @@ import { permutate } from '../PermutateString'
 
 describe('Permutate a string', () => {
   it('expects to throw an Error with an empty string', () => {
-    expect(() => { permutate() }).toThrow('The arg must be a valid, non empty string')
+    expect(() => {
+      permutate()
+    }).toThrow('The arg must be a valid, non empty string')
   })
   it('expects to permute "no" into [no, on]', () => {
     expect(['no', 'on']).toEqual(permutate('no'))
@@ -11,7 +13,19 @@ describe('Permutate a string', () => {
     expect(['esy', 'eys', 'sey', 'sye', 'yes', 'yse']).toEqual(permutate('yes'))
   })
   it('expects to permute "good" into [dgoo dogo doog gdoo godo good odgo odog ogdo ogod oodg oogd ]', () => {
-    expect(['dgoo', 'dogo', 'doog', 'gdoo', 'godo', 'good', 'odgo', 'odog', 'ogdo', 'ogod', 'oodg', 'oogd'])
-      .toEqual(permutate('good'))
+    expect([
+      'dgoo',
+      'dogo',
+      'doog',
+      'gdoo',
+      'godo',
+      'good',
+      'odgo',
+      'odog',
+      'ogdo',
+      'ogod',
+      'oodg',
+      'oogd'
+    ]).toEqual(permutate('good'))
   })
 })