Extended platform and architecture support for Metacall

MetaCall currently supports Linux (GCC), Windows (MSVC), and macOS but many platforms where developers want polyglot runtime support are missing.The core layers have partial support for some platforms but no CI, no environment script integration, and no testing to verify they actually work.Follow TDD approach: set up CI first , then fix environment script + build system, then fix test failures.I will go platform by platform for implementation.All platform logic lives in metacall-environment.sh there will be no hardcoded logic in CI YAML. 8 platform targets with CI pipelines with working environment script section, verified CMake detection and build, automated testing.Fixes to metacall/plthook fork for platforms that need it.