Add CPack packaging & GitHub Release support

Why:
We need to ship METIS as .tar.gz/.zip archives and automatically publish them when a new tag is pushed.

What to do:

1. CMakeLists.txt

   • include(InstallRequiredSystemLibraries) + include(CPack)
   • Set CPACK_PACKAGE_NAME, CPACK_PACKAGE_VERSION, CPACK_GENERATOR = "TGZ;ZIP"
   • Point CPACK_RESOURCE_FILE_README & CPACK_RESOURCE_FILE_LICENSE

2. CI (.github/workflows/ci.yml)

   • After cmake --build, run cpack in each build directory
   • Upload resulting archives as workflow artifacts
   • Add a release job on tag push that uses softprops/action-gh-release to attach those packages

Done when:

• cpack emits both .tar.gz and .zip in build/<preset>/
• CI artifacts include them
• Pushing vX.Y.Z creates a GitHub Release with the packages