update(1): node version update

[aks96]

Description

This PR establishes the foundation for migrating from openid-client v4 to v6 by updating the project to require Node.js 20+ and removing legacy compatibility dependencies. This is the first step in a multi-phase migration plan.

Changes

• Updated Node.js engine requirement: Changed from ^10.19.0 || >=12.0.0 < 13 || >=13.7.0 < 14 || >= 14.2.0 to >=20.0.0
• Updated TypeScript types: Bumped @types/node from ^18.19.119 to ^20.0.0
• Unpinned nock version: Updated from ^11.9.1 to ^13.0.0 for better Node.js 20+ compatibility
• Updated GitHub Actions: Changed base Node.js version from 18 to 20 in CI workflow