feat 🥁: add ESLint v9 extends field support and document 8.57.0 compatibility

- confirm compatibility with ESLint 8.57.0
- add support for ESLint v9 extends field in flat config
- maintain backward compatibility with existing usage patterns
- update docs with configuration examples

This commit enhances the plugin's configuration options for ESLint v9 users while
ensuring backward compatibility. Users can now use the familiar extends syntax
with flat config, simplifying integration into existing projects. Documentation
has been updated to demonstrate proper usage with both ESLint 8 and 9.

eslint.config.mjs

@@ -1,22 +1,10 @@
-import path from 'path';
-import { fileURLToPath } from 'url';
-import { FlatCompat } from '@eslint/eslintrc';
 import eslintPluginESLintPlugin from 'eslint-plugin-eslint-plugin';
 import importPlugin from 'eslint-plugin-import';
+import { defineConfig } from 'eslint/config';
+import prettierConfig from 'eslint-config-prettier';
 import * as tseslint from 'typescript-eslint';
 
-// mimic CommonJS variables
-const __filename = fileURLToPath(import.meta.url);
-const __dirname = path.dirname(__filename);
-
-const compat = new FlatCompat({
-  baseDirectory: __dirname,
-});
-
-export default [
-  // mimic ESLintRC-style extends
-  // Prettier always must be last to override other style rules
-  ...compat.extends('prettier'),
+export default defineConfig([
   {
     files: ['**/*.js', '**/*.ts', '**/*.cjs', '**/*.mjs'],
     plugins: {
@@ -74,6 +62,7 @@ export default [
       'import/export': 'error',
     },
   },
+
   ...tseslint.configs.recommended,
 
   {
@@ -103,4 +92,6 @@ export default [
       'no-unused-vars': 'off',
     },
   },
-];
+
+  prettierConfig,
+]);