Use Vitest and expect methods for testing suite

[yeoffrey]

In this PR, the test suite has been modified:

• deepStrictEqual and deepEqual have been changed to .toStrictEqual for objects and arrays and .toBe for literals.
• Moved the deprecated tests to their own file.
• I've opted to keep the usage of throws and doesNotThrow because it offers a nicer api to check whether an error was thrown or not than the Jesty expect solution.
• Expect documentation from Vitest for your reference!

#1244

[arturmuller]

This is great! Thank you @yeoffrey! 🙌

I would change the throws/doesNotThrow calls as well. Unless we really have to, I would avoid special cases and exceptions — I doubt that new contributors would realise that we use assert for error handling, but Vitest for everything else.

I tested this snippet and it seems to print almost the same exact message like assert, so I don't think we're losing any more functionality.

it('custom error message', () => {
  expect(() => string().create(42, 'Not a string!')).toThrow(
    expect.objectContaining({
      message: 'Not a string!',
      cause: 'Expected a string, but received: 42',
    })
  )
})