Switch unit tests to use vitest

.eslintrc.js

@@ -198,9 +198,7 @@ module.exports = {
     "import/no-deprecated": "error",
     "import/no-extraneous-dependencies": [
       "error",
-      {
-        devDependencies: false,
-      },
+      { devDependencies: ["**/*.test.ts", "**/__tests__/**"] },
     ],
     "import/no-internal-modules": "off",
     "import/order": [

FILES.md

@@ -183,9 +183,7 @@ The rx-player contains multiple type of tests:
 - unit tests: test specific parts of the code. The main goal here is to check the
   implementation of smaller units of code.
 
-  They are written alongside the code, in `__tests__` directories. All its configuration
-  can be found at the root of the project, in `jest.config.js` (we use the jest library
-  for unit tests).
+  They are written alongside the code, in `__tests__` directories.
 
 - memory tests: test the memory usage of the player.