feat: drop support for PHP < 8.1

allow PHPUnit 10/11,
allow "spatie/phpunit-snapshot-assertions" 5

src/Common/BitUtils.php

@@ -11,6 +11,10 @@
  */
 final class BitUtils
 {
+    private function __construct()
+    {
+    }
+
     /**
      * Performs an unsigned right shift.
      *

src/Encoder/MaskUtil.php

@@ -20,6 +20,10 @@ final class MaskUtil
     public const N4 = 10;
     /**#@-*/
 
+    private function __construct()
+    {
+    }
+
     /**
      * Applies mask penalty rule 1 and returns the penalty.
      *

src/Renderer/Eye/SimpleCircleEye.php

@@ -12,6 +12,10 @@ final class SimpleCircleEye implements EyeInterface
 {
     private static ?SimpleCircleEye $instance;
 
+    private function __construct()
+    {
+    }
+
     public static function instance() : self
     {
         return self::$instance ?: self::$instance = new self();

src/Renderer/Eye/SquareEye.php

@@ -12,6 +12,10 @@ final class SquareEye implements EyeInterface
 {
     private static ?SquareEye $instance;
 
+    private function __construct()
+    {
+    }
+
     public static function instance() : self
     {
         return self::$instance ?: self::$instance = new self();

src/Renderer/Module/SquareModule.php

@@ -14,6 +14,10 @@ final class SquareModule implements ModuleInterface
 {
     private static ?SquareModule $instance;
 
+    private function __construct()
+    {
+    }
+
     public static function instance() : self
     {
         return self::$instance ?: self::$instance = new self();

src/Renderer/Path/Close.php

@@ -7,6 +7,10 @@ final class Close implements OperationInterface
 {
     private static ?Close $instance;
 
+    private function __construct()
+    {
+    }
+
     public static function instance() : self
     {
         return self::$instance ?: self::$instance = new self();