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/Linked-List/CycleDetection.js

@@ -3,18 +3,22 @@
  * https://en.wikipedia.org/wiki/Cycle_detection
  */
 
-function detectCycle (head) {
+function detectCycle(head) {
   /*
   Problem Statement:
   Given head, the head of a linked list, determine if the linked list has a cycle in it.
   Link for the Problem: https://leetcode.com/problems/linked-list-cycle/
   */
-  if (!head) { return false }
+  if (!head) {
+    return false
+  }
 
   let slow = head
   let fast = head.next
   while (fast && fast.next) {
-    if (fast === slow) { return true }
+    if (fast === slow) {
+      return true
+    }
     fast = fast.next.next
     slow = slow.next
   }