WIP: use native overflow checks and expand CI coverage

[uvlad7]

Native overflow checks

• Uses C23 ckd_add and ckd_mul whenever <stdckdint.h> is available.
• Otherwise uses __builtin_add_overflow and __builtin_mul_overflow when Clang advertises them or GCC 5+ is used.
• Uses MSVC x64 _addcarry_u64 and _umul128; MSVC ARM64 uses __umulh for multiplication and the portable carry check for addition.
• Retains portable arithmetic fallbacks for unsupported compilers.

CI coverage

• Keeps the existing Ubuntu Ruby-version matrix.
• Adds Ruby 3.4.10 jobs for macOS latest, macOS 15 Intel, Ubuntu 24.04 ARM, Windows 2022, Windows 2025, and Windows 11 ARM.
• Adds an MSWIN Ruby job on Windows 2025.
• Runs Valgrind on Ubuntu ARM as well as the existing supported Linux jobs.

Dependencies

• Replaces the Ubuntu-only apt action with ruby/setup-ruby-pkgs.
• Installs YAJL using apt, Homebrew (with _update_), MSYS2 MinGW, and vcpkg for MSWIN.
• Passes vcpkg action OPT_DIR through to extconf so mkmf locates YAJL headers and libraries; the action adds only its DLL directory to PATH.

Verification

• Ruby 4.1: 55 examples, 0 failures.
• RuboCop and local workflow YAML parsing pass.

Draft pending GitHub Actions results across the new runners.