chore: Node.js maintenance update

[azu]

Summary

This PR performs routine Node.js maintenance updates for the repository:

• Migrated from yarn v1 to pnpm for better dependency management
• Updated Node.js versions in CI to use LTS versions (20, 22, 24)
• Cleaned up release workflow after pnpm migration

Changes Made

1. Package Manager Migration

   • Converted from yarn v1 to pnpm
   • Updated all GitHub Actions workflows to use pnpm
   • Added packageManager field to package.json

2. CI Updates

   • Updated test matrix to use Node.js 20, 22, and 24
   • Pinned all GitHub Actions to specific SHAs for security
   • Removed obsolete npm version check from release workflow

3. Release Workflow Improvements

   • Fixed references from "pnpm package" to "npm package" in comments
   • Removed unnecessary npm version check (pnpm handles this)

Testing

• CI tests pass with new Node.js versions
• Release workflow functions correctly with pnpm
• All GitHub Actions are properly pinned

Checklist

• Migrated from yarn v1 to pnpm
• Updated Node.js versions in GitHub Actions
• Verified all actions are pinned with SHA
• No Node.js 18 references remain in workflows
• Applied Type: Maintenance label