Make const element proxy. #554

Job	Run time
CMake Matrix Test. (Linux Min GCC, ubuntu-22.04, gcc-12, g++-12, 3.9, 3.19.x, ON, OFF, static)	17m 2s
CMake Matrix Test. (Linux Min GCC, ubuntu-22.04, gcc-12, g++-12, 3.9, 3.19.x, ON, OFF, shared)	12m 57s
CMake Matrix Test. (Linux Min Clang, ubuntu-22.04, clang-12, clang++-12, 3.9, 3.19.x, ON, OFF, st...	13m 16s
CMake Matrix Test. (Linux Min Clang, ubuntu-22.04, clang-12, clang++-12, 3.9, 3.19.x, ON, OFF, sh...	12m 48s
CMake Matrix Test. (MacOS Min, macos-12, clang, clang++, 3.9, 3.19.x, ON, OFF, static)	14m 18s
CMake Matrix Test. (MacOS Min, macos-12, clang, clang++, 3.9, 3.19.x, ON, OFF, shared)	9m 42s
CMake Matrix Test. (Linux Max GCC, ubuntu-24.04, gcc-14, g++-14, 3.12, 3.22.x, ON, OFF, static)	29m 38s
CMake Matrix Test. (Linux Max GCC, ubuntu-24.04, gcc-14, g++-14, 3.12, 3.22.x, ON, OFF, shared)	21m 9s
CMake Matrix Test. (Linux SIMD, ubuntu-24.04, gcc-14, g++-14, 3.12, 3.22.x, OFF, ON, static)	29m 13s
CMake Matrix Test. (Linux SIMD, ubuntu-24.04, gcc-14, g++-14, 3.12, 3.22.x, OFF, ON, shared)	21m 1s
CMake Matrix Test. (Linux Max Clang, ubuntu-24.04, clang-18, clang++-18, 3.12, 3.22.x, ON, OFF, s...	17m 11s
CMake Matrix Test. (Linux Max Clang, ubuntu-24.04, clang-18, clang++-18, 3.12, 3.22.x, ON, OFF, s...	13m 57s
CMake Matrix Test. (MacOS Max, macos-14, clang, clang++, 3.12, 3.22.x, ON, OFF, static)	13m 25s
CMake Matrix Test. (MacOS Max, macos-14, clang, clang++, 3.12, 3.22.x, ON, OFF, shared)	7m 48s
	3h 53m 25s

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