Allow psr/http-message:^2

Also allow expected composer plugins and set minimum php version to keep lockfile compatible with lowest supported version .

Adds parameter and return type hints to all test stubs for psr/http-message v2 compatibility. Some tests will fail due to incompatible signatures when deps are at lowest.

Author: gsteel

composer.json

@@ -9,10 +9,19 @@
             "email": "[email protected]"
         }
     ],
+    "config": {
+        "allow-plugins": {
+            "dealerdirect/phpcodesniffer-composer-installer": true,
+            "phpstan/extension-installer": true
+        },
+        "platform": {
+            "php": "7.2.99"
+        }
+    },
     "require": {
         "php": "^7.2 || ^8.0",
         "ext-pcre": "*",
-        "psr/http-message": "^1"
+        "psr/http-message": "^1.0.1 || ^2"
     },
     "autoload": {
         "psr-4": {