Allow psr/http-message ^2.0 (#25)

* Add psr/http-message ^2.0 to composer.json
* Additionally remove unused imports

Author: marein

composer.json

@@ -22,7 +22,7 @@
     "php": "^7.4 || ^8.0",
     "ext-json": "*",
     "psr/http-client": "^1.0",
-    "psr/http-message": "^1.0",
+    "psr/http-message": "^1.0 || ^2.0",
     "psr/http-factory": "^1.0"
   },
   "require-dev": {

tests/Integration/HttpAdapter/ClientTestCase.php

@@ -8,8 +8,6 @@
 use Marein\Nchan\Http\Client;
 use Marein\Nchan\Http\Request;
 use Marein\Nchan\Http\Url;
-use Marein\Nchan\HttpAdapter\Credentials;
-use Marein\Nchan\HttpAdapter\HttpStreamWrapperClient;
 use PHPUnit\Framework\TestCase;
 
 abstract class ClientTestCase extends TestCase