Allow a GuzzleResponse body to be queried more than once

- Using `StreamInterface->getContents` left the stream index at the end of the stream, which made every subsequent call to `getBody()` return empty string
- Using `StreamInterface->__toString()` magic method correctly seek the stream to the start before reading

src/Network/GuzzleResponse.php

@@ -147,8 +147,8 @@ class GuzzleResponse extends Response implements IHTTPResult, ResponseInterface
 	}
 
 	/// @todo - fix mismatching use of "getBody()" as string here and parent "getBody()" as streaminterface
-	public function getBody()
+	public function getBody(): string
 	{
-		return parent::getBody()->getContents();
+		return (string) parent::getBody();
 	}
 }