M1 Mac Build

[hugofloresgarcia]

building for M1 mac will fail using the current build instructions, since Conan does not have an arm build of pytorch that it can grab and link to automatically. Instead, we have to download m1 libtorch from here: https://github.com/mlverse/libtorch-mac-m1 and manually make that visible to CMake via environment variables. This should either be made clear in the documentation, or it should be fixed so that the m1 libtorch build is downloaded automatically through Conan