Add SCons variant_dir support #219

Job	Run time
📊 Static Checks / Format (clang-format, ruff format, file format)	14s
🛠️ Continuous Integration / 🐧 Build (Linux, GCC, CMake Ninja)	23m 1s
🛠️ Continuous Integration / 🏁 Build (Windows, MSVC, CMake)	24m 26s
🛠️ Continuous Integration / 🐧 Linux (GCC)	1m 4s
🛠️ Continuous Integration / 🐧 Linux (GCC, Double Precision)	59s
🛠️ Continuous Integration / 🏁 Windows (x86_64, MSVC)	2m 17s
🛠️ Continuous Integration / 🏁 Windows (x86_64, MinGW)	38m 46s
🛠️ Continuous Integration / 🍎 macOS (universal)	48s
🛠️ Continuous Integration / 🤖 Android (arm64)	1m 22s
🛠️ Continuous Integration / 🍏 iOS (arm64)	51s
🛠️ Continuous Integration / 🌐 Web (wasm32)	1m 6s
	1h 34m 54s

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