Improved connection handshake session (#1431)

* Added pipelining for on-connection commands

* Added server version condition for tests

* Fixed static analysis and codestyle errors

* Improved handshake session

* Updated HELLO retry logic

* Changed incorrect variable

* Added return statement

* Added more test coverage, codestyle fixes

src/Connection/RelayConnection.php

@@ -369,4 +369,12 @@ class RelayConnection extends AbstractConnection
 
         return $parameters;
     }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function write(string $buffer): void
+    {
+        throw new NotSupportedException('The "relay" extension does not support writing operations.');
+    }
 }