dep(eslint): upgrade to v9

eslint.config.mjs

@@ -0,0 +1,39 @@
+import haraka from "eslint-plugin-haraka";
+import globals from "globals";
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+import js from "@eslint/js";
+import { FlatCompat } from "@eslint/eslintrc";
+
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = path.dirname(__filename);
+const compat = new FlatCompat({
+    baseDirectory: __dirname,
+    recommendedConfig: js.configs.recommended,
+    allConfig: js.configs.all
+});
+
+export default [...compat.extends("eslint:recommended", "plugin:haraka/recommended"), {
+    plugins: {
+        haraka,
+    },
+
+    languageOptions: {
+        globals: {
+            ...globals.node,
+            ...globals.mocha,
+            OK: true,
+            CONT: true,
+            DENY: true,
+            DENYSOFT: true,
+            DENYDISCONNECT: true,
+            DENYSOFTDISCONNECT: true,
+        },
+    },
+
+    rules: {
+        indent: ["error", 2, {
+            SwitchCase: 1,
+        }],
+    },
+}];