feat: allow creating PRedis with a client

[Iandenh]

This pull request introduces the ability to create a PRedis instance using an already initialized Predis\Client. A new static method createWithClient has been added to facilitate this functionality.

Use Case
If a user already has a configured Predis\Client instance, they can now pass it directly to the PRedis class. This avoids the need to reconfigure the client or duplicate configuration logic. For example, I want to pass through enqueue because I have a predis client configured with Sentinel.

Changes

1. Added a check in the constructor to accept a client key in the configuration array. If provided, it validates that the value is an instance of Predis\Client and uses it directly.
2. Added a static method createWithClient(Client $client): self to simplify the creation of a PRedis instance with an existing Predis\Client.

Example Usage

use Predis\Client;
use Enqueue\Redis\PRedis;

$predisClient = new Client(['host' => '127.0.0.1', 'port' => 6379]);
$predis = PRedis::createWithClient($predisClient);

// Pass the PRedis instance to the RedisConnectionFactory
$connectionFactory = new RedisConnectionFactory($predis);

// Get the RedisContext
$redisContext = $connectionFactory->createContext();