feat: support ESLint 9

BREAKING CHANGE:

Requires Node 18

Also:
- chore: use flat config

eslint.config.mjs

@@ -0,0 +1,50 @@
+// import auto from 'eslint-config-canonical/configurations/auto.js';
+import eslintPluginCanonical from './dist/src/index.js';
+
+export default [
+  {
+    ignores: [
+      'package-lock.json',
+      '**/ExportMap.ts',
+      'tests/fixtures',
+
+      'coverage',
+      'dist',
+      'node_modules',
+      'pnpm-lock.yaml',
+      '*.log',
+      '.*',
+      '!.github',
+      '!.gitignore',
+      '!.husky',
+      '!.releaserc',
+    ],
+  },
+  eslintPluginCanonical.configs['flat/recommended'],
+  // ...auto,
+];
+
+/*
+  'overrides': [
+    {
+      'extends': [
+        'canonical',
+        'canonical/node',
+        'canonical/typescript',
+        'canonical/typescript-disable-type-checking',
+        'canonical/prettier'
+      ],
+      'rules': {
+        'unicorn/expiring-todo-comments': 0,
+        '@typescript-eslint/no-for-in-array': 0
+      },
+      'files': '*.ts'
+    },
+    {
+      'extends': [
+        'canonical/json'
+      ],
+      files: ['*.json']
+    }
+  ]
+*/