make sure we can convert Request and Notification to string

This is already used when we are logging

Author: Nyholm

src/Message/Notification.php

@@ -37,4 +37,9 @@ public function jsonSerialize(): array
             'params' => $this->params,
         ];
     }
+
+    public function __toString(): string
+    {
+        return sprintf('%s', $this->method);
+    }
 }

src/Message/Request.php

@@ -40,4 +40,9 @@ public function jsonSerialize(): array
             'params' => $this->params,
         ];
     }
+
+    public function __toString(): string
+    {
+        return sprintf('%s: %s', $this->id, $this->method);
+    }
 }