TASK: Add shell.nix for local testing

shell.nix

@@ -0,0 +1,65 @@
+{ pkgs ? import <nixpkgs> { } }:
+
+let
+  php = pkgs.php82.buildEnv {
+    extensions = { enabled, all }: enabled ++ (with all; [
+      xdebug
+    ]);
+
+    extraConfig = ''
+      xdebug.mode = debug
+      memory_limit = 4G
+    '';
+  };
+  inherit(pkgs.php82Packages) composer;
+
+  projectInstall = pkgs.writeShellApplication {
+    name = "project-install";
+    runtimeInputs = [
+      php
+      composer
+    ];
+    text = ''
+      rm -rf .Build/ vendor/ composer.lock
+      composer update --prefer-dist --no-progress --working-dir="$PROJECT_ROOT"
+    '';
+  };
+
+  projectCgl = pkgs.writeShellApplication {
+    name = "project-cgl";
+
+    runtimeInputs = [
+      php
+    ];
+
+    text = ''
+      PHP_CS_FIXER_IGNORE_ENV=1 ./vendor/bin/php-cs-fixer fix --dry-run --diff
+    '';
+  };
+
+  projectCglFix = pkgs.writeShellApplication {
+    name = "project-cgl-fix";
+
+    runtimeInputs = [
+      php
+    ];
+
+    text = ''
+      PHP_CS_FIXER_IGNORE_ENV=1 ./vendor/bin/php-cs-fixer fix
+    '';
+  };
+
+in pkgs.mkShell {
+  name = "TYPO3 Extension Responsive Images";
+  buildInputs = [
+    php
+    composer
+    projectInstall
+    projectCgl
+    projectCglFix
+  ];
+
+  shellHook = ''
+    export PROJECT_ROOT="$(pwd)"
+  '';
+}