Migrate to ESLint 9 flat config and add Prettier config

[cusxy]

Summary

• Migrate ESLint to v9 flat config: Replace legacy .eslintrc.js with eslint.config.js using ESLint 9's flat config format
• Remove @babel/eslint-parser: The project uses plain JavaScript with no experimental syntax, so the built-in ESLint parser is sufficient
• Add .prettierrc: Explicit Prettier configuration (tabWidth: 2, printWidth: 150, semi: true, singleQuote: false) replacing inline CLI flags
• Update lint:fix script: Use proper quoted glob pattern and rely on .prettierrc instead of CLI flags
• Add new devDependencies: @eslint/js, globals, prettier
• Remove "use strict" class body statements: These were no-ops inside ES2015+ class bodies
• Apply consistent formatting: Prettier reformatted source files to match the new 2-space / 150-char-width config

Details

ESLint Config (eslint.config.js)

• Uses @eslint/js recommended rules
• ecmaVersion: 2022, sourceType: "commonjs" (corrects the old config which incorrectly had sourceType: "module")
• Separate config block for test files with globals.mocha
• Proper ignore patterns for node_modules/, coverage/, .nyc_output/

Removed Dependencies

• @babel/eslint-parser (and its transitive dep @nicolo-ribaudo/eslint-scope-5-internals)

Added Dependencies

• @eslint/js ^9.39.4
• globals ^17.4.0
• prettier ^3.8.1

Test plan

• npm test — all 9 tests passing
• npm run lint:fix — runs cleanly with no changes needed

🤖 Generated with Claude Code