Ban foreach(arrayWithStringKeys as k => v)

this is not as good as phpstan/phpstan-src#769 (e.g. array_key_first()/array_key_last() aren't covered by this, nor is array_rand()) but it does eliminate the most infuriating cases where this usually crops up.

src/utils/Utils.php

@@ -571,6 +571,22 @@ final class Utils{
 		}
 	}
 
+	/**
+	 * Generator which forces array keys to string during iteration.
+	 * This is necessary because PHP has an anti-feature where it casts numeric string keys to integers, leading to
+	 * various crashes.
+	 *
+	 * @phpstan-template TKeyType of string
+	 * @phpstan-template TValueType
+	 * @phpstan-param array<TKeyType, TValueType> $array
+	 * @phpstan-return \Generator<TKeyType, TValueType, void, void>
+	 */
+	public static function stringifyKeys(array $array) : \Generator{
+		foreach($array as $key => $value){ // @phpstan-ignore-line - this is where we fix the stupid bullshit with array keys :)
+			yield (string) $key => $value;
+		}
+	}
+
 	public static function checkUTF8(string $string) : void{
 		if(!mb_check_encoding($string, 'UTF-8')){
 			throw new \InvalidArgumentException("Text must be valid UTF-8");