Summary

Upgrade ESLint from v8 to v9 to support the latest features and enable eslint-typegen integration.

Motivation

• Required for eslint-typegen compatibility (depends on ESLint v9)
• Better compatibility with modern tooling ecosystem

Changes needed

• Upgrade ESLint to v9.x
• Update @typescript-eslint/parser to v8.x for compatibility
• Update @types/eslint to v9.x
• Fix TypeScript compilation errors due to @typescript-eslint API

Related work

This upgrade is a prerequisite for eslint-typegen integration which will provide TypeScript definitions and IntelliSense for ESLint rule configurations. (#2757)