chore: phpstan integration

.gitignore

+tools/
+phpstan.neon
+.phpunit.result.cache
+phpunit.xml
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.phive/phars.xml

+<?xml version="1.0" encoding="UTF-8"?>
+<phive xmlns="https://phar.io/phive">
+  <phar name="phpstan" version="^1.10.67" installed="1.10.67" location="./tools/phpstan" copy="false"/>
+</phive>

phpstan.dist.neon

+includes:
+    - phpstan-baseline.neon
+
+parameters:
+    level: 1
+    paths:
+        - src
+        - ajax
+    bootstrapFiles:
+        - tests/phpstan-bootstrap.php
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tests/phpstan-bootstrap.php

+<?php
+
+if (!defined('QUIQQER_SYSTEM')) {
+    define('QUIQQER_SYSTEM', true);
+}
+
+if (!defined('QUIQQER_AJAX')) {
+    define('QUIQQER_AJAX', true);
+}
+
+putenv("QUIQQER_OTHER_AUTOLOADERS=KEEP");
+
+require_once __DIR__ . '/../../../../bootstrap.php';