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>

Dynamic-Programming/tests/LongestCommonSubsequence.test.js

@@ -26,7 +26,11 @@ describe('LongestCommonSubsequence', () => {
   })
 
   it('expects to return the longest common subsequence, medium-length inputs', () => {
-    expect(longestCommonSubsequence('bsbininm', 'jmjkbkjkv')).toEqual('b'.length)
-    expect(longestCommonSubsequence('oxcpqrsvwf', 'shmtulqrypy')).toEqual('qr'.length)
+    expect(longestCommonSubsequence('bsbininm', 'jmjkbkjkv')).toEqual(
+      'b'.length
+    )
+    expect(longestCommonSubsequence('oxcpqrsvwf', 'shmtulqrypy')).toEqual(
+      'qr'.length
+    )
   })
 })