Generalize values annotation into provider handling

[thekid]

This pull request introduces a generalized Provider annotation, allowing for various implementations

Value-driven tests

#[Values] becomes one of these implementations. Its usage does not change, the following example from our README continues to work!

use test\{Assert, Test, Values};

class CalculatorTest {

  #[Test, Values([[0, 0], [1, 1], [-1, 1]])]
  public function addition($a, $b) {
    Assert::equals($a + $b, (new Calculator())->add($a, $b));
  }
}

Example provider

Implementations must specify a values() method:

use test\Provider;
use lang\reflection\Type;

class StartServer implements Provider {
  private $connection;

  /** Starts a new server */
  public function __construct(string $bind, ?int $port= null) {
    $port??= rand(1024, 65535);
    $this->connection= "Socket({$bind}:{$port})"; // TODO: Actual implementation ;)
  }

  /**
   * Returns values
   *
   * @param  Type $type
   * @param  ?object $instance
   * @return iterable
   */
  public function values($type, $instance= null) {
    return [$this->connection];
  }
}

Used on test case

Provider values are passed as method argument, just like #[Values], the previous only implementation.

use test\{Assert, Test};

class ServerTest {

  #[Test, StartServer('0.0.0.0', 8080)]
  public function connect($connection) {
    Assert::equals('Socket(0.0.0.0:8080)', $connection);
  }
}

Used on test group

Provider values are passed to the constructor and the connection can be used for all test cases. Note: The provider's values() method is invoked with $instance= null!

use test\{Assert, Test};

#[StartServer('0.0.0.0', 8080)]
class ServerTest {

  public function __construct(private $connection) { }

  #[Test]
  public function connect() {
    Assert::equals('Socket(0.0.0.0:8080)', $this->connection);
  }
}