Avoid downloading the history of binaries

[eliemichel]

When fetching the wgpu-native branch, we should get it as a zip rather than cloning the repository

[eliemichel]

It is better now that everything has been reorganized into a single main branch that only contains CMake files. The repo is bloatted up by old branches though, I will remove them once I'm certain enough that nobody relies on them any more (i.e., when I remove any reference to them in the LearnWebGPU guide)