Add SCons variant_dir support #172

Job	Run time
📊 Static Checks / Format (clang-format, ruff format, file format)	15s
🛠️ Continuous Integration / 🐧 Build (Linux, GCC, CMake Ninja)	22m 6s
🛠️ Continuous Integration / 🏁 Build (Windows, MSVC, CMake)	24m 58s
🛠️ Continuous Integration / 🐧 Linux (GCC)	1m 18s
🛠️ Continuous Integration / 🐧 Linux (GCC, Double Precision)	1m 19s
🛠️ Continuous Integration / 🏁 Windows (x86_64, MSVC)	1m 58s
🛠️ Continuous Integration / 🏁 Windows (x86_64, MinGW)	35m 22s
🛠️ Continuous Integration / 🍎 macOS (universal)	1m 1s
🛠️ Continuous Integration / 🤖 Android (arm64)	1m 11s
🛠️ Continuous Integration / 🍏 iOS (arm64)	44s
🛠️ Continuous Integration / 🌐 Web (wasm32)	1m 3s
	1h 31m 15s

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