Push notifications support (#1316)

* Added new push notifications consumer

* Added push notifications dispatcher loop, intoduced consumer and dispatcher interfaces

* Static analysis fixes

* Codestyle fix

* Codestyle fixes

* Moved RelayConsumer in appropriate directory, fixed access modifiers

src/Consumer/ConsumerInterface.php

@@ -0,0 +1,64 @@
+<?php
+
+/*
+ * This file is part of the Predis package.
+ *
+ * (c) 2009-2020 Daniele Alessandri
+ * (c) 2021-2023 Till Krüss
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Predis\Consumer;
+
+use Iterator;
+use Predis\ClientInterface;
+use ReturnTypeWillChange;
+
+interface ConsumerInterface extends Iterator
+{
+    /**
+     * @param ClientInterface $client
+     */
+    public function __construct(ClientInterface $client);
+
+    /**
+     * Stops consumer loop, with optional client disconnection.
+     *
+     * @param  bool $drop
+     * @return bool
+     */
+    public function stop(bool $drop = false): bool;
+
+    /**
+     * Returns consumer client instance.
+     *
+     * @return ClientInterface
+     */
+    public function getClient(): ClientInterface;
+
+    /**
+     * Returns last payload produced by server.
+     *
+     * @return mixed
+     */
+    #[ReturnTypeWillChange]
+    public function current();
+
+    /**
+     * Keeps loop until consumer is in valid state.
+     *
+     * @return void
+     */
+    #[ReturnTypeWillChange]
+    public function next();
+
+    /**
+     * Checks if consumer is in the valid state to continue.
+     *
+     * @return bool
+     */
+    #[ReturnTypeWillChange]
+    public function valid();
+}