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>

Maths/test/IsDivisible.test.js

@@ -17,9 +17,12 @@ describe('isDivisible', () => {
     [5, -0, false]
   ]
 
-  test.each(testCases)('if parameters are (%i, %i) it returns %p', (dividend, divisor, expected) => {
-    expect(isDivisible(dividend, divisor)).toBe(expected)
-  })
+  test.each(testCases)(
+    'if parameters are (%i, %i) it returns %p',
+    (dividend, divisor, expected) => {
+      expect(isDivisible(dividend, divisor)).toBe(expected)
+    }
+  )
 
   const errorCases = [
     [NaN, NaN],
@@ -31,9 +34,12 @@ describe('isDivisible', () => {
     [false, 2]
   ]
 
-  test.each(errorCases)('throws an error if parameters are (%p, %p)', (dividend, divisor) => {
-    expect(() => {
-      isDivisible(dividend, divisor)
-    }).toThrow()
-  })
+  test.each(errorCases)(
+    'throws an error if parameters are (%p, %p)',
+    (dividend, divisor) => {
+      expect(() => {
+        isDivisible(dividend, divisor)
+      }).toThrow()
+    }
+  )
 })