chore: add code quality tools

tools/phpstan/.gitignore

@@ -0,0 +1 @@
+/vendor

tools/phpstan/composer.json

@@ -0,0 +1,5 @@
+{
+    "require": {
+        "phpstan/phpstan": "^1.8"
+    }
+}

tools/phpstan/composer.lock

@@ -0,0 +1,78 @@
+{
+    "_readme": [
+        "This file locks the dependencies of your project to a known state",
+        "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
+        "This file is @generated automatically"
+    ],
+    "content-hash": "694b48ce16f1016ff299766be0c7a4ba",
+    "packages": [
+        {
+            "name": "phpstan/phpstan",
+            "version": "1.8.2",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/phpstan/phpstan.git",
+                "reference": "c53312ecc575caf07b0e90dee43883fdf90ca67c"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/phpstan/phpstan/zipball/c53312ecc575caf07b0e90dee43883fdf90ca67c",
+                "reference": "c53312ecc575caf07b0e90dee43883fdf90ca67c",
+                "shasum": ""
+            },
+            "require": {
+                "php": "^7.2|^8.0"
+            },
+            "conflict": {
+                "phpstan/phpstan-shim": "*"
+            },
+            "bin": [
+                "phpstan",
+                "phpstan.phar"
+            ],
+            "type": "library",
+            "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/1.8.2"
+            },
+            "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": "2022-07-20T09:57:31+00:00"
+        }
+    ],
+    "packages-dev": [],
+    "aliases": [],
+    "minimum-stability": "stable",
+    "stability-flags": [],
+    "prefer-stable": false,
+    "prefer-lowest": false,
+    "platform": [],
+    "platform-dev": [],
+    "plugin-api-version": "2.3.0"
+}