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/CheckAnagram.test.js

@@ -12,9 +12,7 @@ describe('Testing checkAnagramRegex', () => {
   `(
     'expects to throw the type Error given values $inputOne and $inputTwo',
     ({ inputOne, inputTwo }) => {
-      expect(
-        () => checkAnagramRegex(inputOne, inputTwo)
-      ).toThrowError()
+      expect(() => checkAnagramRegex(inputOne, inputTwo)).toThrowError()
     }
   )
 
@@ -102,9 +100,7 @@ describe('Testing checkAnagramMap', () => {
   `(
     'expects to throw the type Error given values $inputOne and $inputTwo',
     ({ inputOne, inputTwo }) => {
-      expect(
-        () => checkAnagramMap(inputOne, inputTwo)
-      ).toThrowError()
+      expect(() => checkAnagramMap(inputOne, inputTwo)).toThrowError()
     }
   )