[codex] Speed up Windows release builds

[Samuel-Mencke]

Summary

• caps CI node-gyp job parallelism to a safer default
• adds native package concurrency for the Windows release runner
• documents the CI-only tuning knobs while keeping local defaults conservative

Testing

• PowerShell parser check for scripts/build-pointer-release.ps1
• git diff --check
• build/typecheck already passed before cherry-picking these commits

Release note

This should reduce time spent in Windows native rebuilds without asking contributors to run heavy local builds.