Update ESLint for lint npm task

Wew update ES lint to check against ECMAScript 2020, and use the new config format

eslint.config.js

@@ -0,0 +1,40 @@
+import prettier from "eslint-plugin-prettier";
+import jest from "eslint-plugin-jest";
+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"),
+  {
+    plugins: {
+      prettier,
+      jest,
+    },
+
+    languageOptions: {
+      globals: {
+        ...globals.node,
+        ...jest.environments.globals.globals,
+      },
+
+      ecmaVersion: 2020,
+    },
+
+    rules: {
+      "prettier/prettier": ["error", {}],
+      "no-unused-vars": "off",
+    },
+  },
+];