Mocking exceptions

[Sammyjo20]

Introduces the ability to mock exceptions, including Guzzle exceptions, like ConnectException.

For example:

$mockClient = new MockClient([
    MockResponse::make(['name' => 'Sam'])->throw(new Exception('Custom Exception!')),
]);

// Or using Guzzle

$mockClient = new MockClient([
    MockResponse::make(['name' => 'Sam'])->throw(fn ($guzzleRequest) => new GuzzleException('Cannot connect!', $guzzleRequest)),
]);

[Sammyjo20]

Self review complete