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/CreatePermutations.js

@@ -5,7 +5,7 @@ More at : https://en.wikipedia.org/wiki/Permutation
 */
 
 const createPermutations = (str) => {
-// convert string to array
+  // convert string to array
   const arr = str.split('')
 
   // get array length
@@ -18,7 +18,9 @@ const createPermutations = (str) => {
   let next
 
   // if strLen is zero, return the same string
-  if (strLen === 0) { return [str] }
+  if (strLen === 0) {
+    return [str]
+  }
   // loop to the length to get all permutations
   for (let i = 0; i < strLen; i++) {
     rest = Object.create(arr)