Consider not using cpm-cmake

[Pandapip1]

CPM makes it very hard to build stereokit-rust without network access, means that packagers must rebuild dependencies twice, and means that system dependencies aren't used. Consider switching to libloading.

[mvvvv]

Thank you for trying StereoKit-rust. cpm-cmake is used to build StereoKitC, of ​​which StereoKit-rust is a binding. You can avoid downloading by using the force-local-deps feature and specifying the library path using the environment variables: DEP_OPENXR_LOADER_SOURCE, DEP_MESHOPTIMIZER_SOURCE, DEP_BASIS_UNIVERSAL_SOURCE, and DEP_SK_GPU_SOURCE.

FORCE_LOCAL_DEPS=ON DEP_SK_GPU_SOURCE="/opt/sk_gpu" cargo build_sk_rs --example main_pc --features event-loop,force-local-deps ../sk_builds/SK_demo_linux/