build: Add PHPStan [ci skip]

composer.json

@@ -26,6 +26,7 @@
         "sort-packages": true
     },
     "require-dev": {
+        "phpstan/phpstan": "^0.12.98",
         "phpunit/phpunit": "^9.5"
     },
     "autoload": {

composer.lock

@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "e16352573256967e1714ff2adc994bbf",
+    "content-hash": "ae345e15b82c45a1aca0dbe4473948cb",
     "packages": [
         {
             "name": "dflydev/ant-path-matcher",
@@ -4630,6 +4630,70 @@
             },
             "time": "2021-03-17T13:42:18+00:00"
         },
+        {
+            "name": "phpstan/phpstan",
+            "version": "0.12.98",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/phpstan/phpstan.git",
+                "reference": "3bb7cc246c057405dd5e290c3ecc62ab51d57e00"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/phpstan/phpstan/zipball/3bb7cc246c057405dd5e290c3ecc62ab51d57e00",
+                "reference": "3bb7cc246c057405dd5e290c3ecc62ab51d57e00",
+                "shasum": ""
+            },
+            "require": {
+                "php": "^7.1|^8.0"
+            },
+            "conflict": {
+                "phpstan/phpstan-shim": "*"
+            },
+            "bin": [
+                "phpstan",
+                "phpstan.phar"
+            ],
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "0.12-dev"
+                }
+            },
+            "autoload": {
+                "files": [
+                    "bootstrap.php"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "description": "PHPStan - PHP Static Analysis Tool",
+            "support": {
+                "issues": "https://github.com/phpstan/phpstan/issues",
+                "source": "https://github.com/phpstan/phpstan/tree/0.12.98"
+            },
+            "funding": [
+                {
+                    "url": "https://github.com/ondrejmirtes",
+                    "type": "github"
+                },
+                {
+                    "url": "https://github.com/phpstan",
+                    "type": "github"
+                },
+                {
+                    "url": "https://www.patreon.com/phpstan",
+                    "type": "patreon"
+                },
+                {
+                    "url": "https://tidelift.com/funding/github/packagist/phpstan/phpstan",
+                    "type": "tidelift"
+                }
+            ],
+            "time": "2021-09-02T12:33:01+00:00"
+        },
         {
             "name": "phpunit/php-code-coverage",
             "version": "9.2.6",

phpstan.neon

@@ -0,0 +1,4 @@
+parameters:
+  level: 5
+  paths:
+    - src