[codex] Add package CI and release artifacts

[vinzenz]

Summary

This PR adds dedicated CI coverage for the new package-consumption paths and release-tag package publishing.

Changes

• Adds package consumer CI for installed CMake config, FetchContent, and CPM.cmake usage.
• Adds package-manager CI for the Conan recipe and vcpkg overlay port.
• Extends CPack metadata for Debian and RPM generation.
• Adds an Arch Linux PKGBUILD and a tag-only release workflow that builds .deb, .rpm, archives, and pacman package artifacts.
• Uploads release package artifacts to the matching GitHub release when a v* tag is pushed.

Validation

Local checks run before opening the PR:

• Parsed all workflow YAML files with Python/PyYAML.
• Built and ran the install-tree CMake consumer.
• Built and ran the FetchContent consumer.
• Built and ran the CPM.cmake consumer.
• Generated CPack DEB and TGZ packages locally.

Notes:

• Local RPM generation was not run because this host lacks rpmbuild; the workflow installs the required rpm tooling on Ubuntu.
• Local Arch package validation was blocked by rootless container volume permissions; the workflow uses GitHub-hosted Docker to run makepkg in archlinux:base-devel.