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/Graph/Graph2.js

@@ -2,7 +2,7 @@
 class Graph {
   // defining vertex array and
   // adjacent list
-  constructor (noOfVertices) {
+  constructor(noOfVertices) {
     this.noOfVertices = noOfVertices
     this.AdjList = new Map()
   }
@@ -17,7 +17,7 @@ class Graph {
   // dfs(v)
 
   // add vertex to the graph
-  addVertex (v) {
+  addVertex(v) {
     // initialize the adjacent list with a
     // null array
 
@@ -25,7 +25,7 @@ class Graph {
   }
 
   // add edge to the graph
-  addEdge (v, w) {
+  addEdge(v, w) {
     // get the list for vertex v and put the
     // vertex w denoting edge between v and w
     this.AdjList.get(v).push(w)
@@ -36,7 +36,7 @@ class Graph {
   }
 
   // Prints the vertex and adjacency list
-  printGraph (output = value => console.log(value)) {
+  printGraph(output = (value) => console.log(value)) {
     // get all the vertices
     const getKeys = this.AdjList.keys()