feat: php 8.3, phpunit 11 (#57)

* Upgrade runner php to 8.3, phpunit to 11
* Fix tests, tweaked the code, added missing ext- to composer.json
* Fix exception related code smells

composer.json

@@ -1,7 +1,12 @@
 {
     "name": "ivuorinen/palette",
     "description": "Get most used colors from an image",
-    "keywords": ["image", "colors", "palette", "psr-2"],
+    "keywords": [
+        "image",
+        "colors",
+        "palette",
+        "psr-2"
+    ],
     "homepage": "https://github.com/ivuorinen/palette",
     "type": "library",
     "license": "MIT",
@@ -16,22 +21,27 @@
         "issues": "https://github.com/ivuorinen/palette/issues"
     },
     "autoload": {
-        "psr-0": { "ivuorinen\\Palette\\": "src/" },
-        "classmap": ["src/"]
+        "psr-4": {
+            "ivuorinen\\Palette\\": "src/"
+        }
     },
     "autoload-dev": {
-        "psr-0": {
+        "psr-4": {
             "ivuorinen\\Palette\\Tests\\": "tests/"
         }
     },
     "require": {
-        "php": ">=5.6.0"
+        "php": "^8.3",
+        "ext-gd": "*",
+        "ext-exif": "*"
     },
     "require-dev": {
-        "phpunit/phpunit": "10.5.10",
-        "squizlabs/php_codesniffer": "3.9.0"
+        "phpunit/phpunit": "^11",
+        "squizlabs/php_codesniffer": "^3"
     },
     "scripts": {
-        "test": "vendor/bin/phpunit"
+        "test": "vendor/bin/phpunit",
+        "lint": "vendor/bin/phpcs",
+        "lint-fix": "vendor/bin/phpcbf"
     }
 }