update packages & convert eslint to flat config

eslint.config.mjs

@@ -0,0 +1,55 @@
+// @ts-check
+import eslint from '@eslint/js';
+import tseslint from 'typescript-eslint';
+import eslintPluginSimpleImportSort from 'eslint-plugin-simple-import-sort';
+
+export default tseslint.config(
+  {
+    files: ['src/**/*.ts'],
+    extends: [eslint.configs.recommended, ...tseslint.configs.strict],
+    plugins: {
+      'simple-import-sort': eslintPluginSimpleImportSort,
+    },
+    languageOptions: {
+      parserOptions: {
+        project: true,
+      },
+    },
+    rules: {
+      '@typescript-eslint/explicit-function-return-type': 'warn',
+      '@typescript-eslint/explicit-module-boundary-types': 'off',
+      'no-invalid-this': 'off',
+      '@typescript-eslint/no-invalid-this': 'warn',
+      'no-loop-func': 'off',
+      '@typescript-eslint/no-loop-func': 'warn',
+      'no-redeclare': 'off',
+      '@typescript-eslint/no-redeclare': 'warn',
+      'no-shadow': 'off',
+      '@typescript-eslint/no-shadow': 'warn',
+      'no-use-before-define': 'off',
+      '@typescript-eslint/no-non-null-assertion': 'warn',
+      '@typescript-eslint/no-use-before-define': 'warn',
+      '@typescript-eslint/no-unnecessary-qualifier': 'warn',
+      '@typescript-eslint/prefer-readonly': 'warn',
+      '@typescript-eslint/prefer-regexp-exec': 'warn',
+      'no-return-await': 'off',
+      '@typescript-eslint/return-await': 'warn',
+      '@typescript-eslint/strict-boolean-expressions': 'warn',
+
+      'array-callback-return': 'warn',
+      complexity: ['warn', { max: 15 }],
+      eqeqeq: ['warn', 'always', { null: 'ignore' }],
+      'no-unused-vars': 'warn',
+      'object-shorthand': ['warn', 'always'],
+
+      'simple-import-sort/imports': 'warn',
+    },
+  },
+  {
+    files: ['*.spec.ts', 'test/**/*.ts'],
+    rules: {
+      '@typescript-eslint/no-non-null-assertion': 'off',
+      '@typescript-eslint/explicit-function-return-type': 'off',
+    },
+  }
+);