Migrate ESLint to flat config format (v9) and update CI workflow

eslint.config.js

@@ -0,0 +1,39 @@
+const js = require('@eslint/js');
+const parser = require('@typescript-eslint/parser');
+const plugin = require('@typescript-eslint/eslint-plugin');
+const prettierPlugin = require('eslint-plugin-prettier');
+const prettierConfig = require('eslint-config-prettier');
+
+module.exports = [
+  js.configs.recommended,
+  prettierConfig,
+  {
+    files: ['**/*.ts'],
+    languageOptions: {
+      parser: parser,
+      parserOptions: {
+        project: './tsconfig.json',
+        sourceType: 'module',
+      },
+      globals: {
+        node: true,
+        jest: true,
+      },
+    },
+    plugins: {
+      '@typescript-eslint': plugin,
+      prettier: prettierPlugin,
+    },
+    rules: {
+      ...plugin.configs.recommended.rules,
+      '@typescript-eslint/interface-name-prefix': 'off',
+      '@typescript-eslint/explicit-function-return-type': 'off',
+      '@typescript-eslint/explicit-module-boundary-types': 'off',
+      '@typescript-eslint/no-explicit-any': 'off',
+      'prettier/prettier': 'error',
+    },
+  },
+  {
+    ignores: ['dist/**', 'node_modules/**', 'coverage/**'],
+  },
+];