caching the cargo related files can help build speeds a lot

[Connoropolous]

don't need the nodejs thing because nix is coming with node

i was working on improving all this over in https://github.com/lightningrodlabs/electron-holochain-template

could also add caching of node_modules with pnpm-lock file as the cache busting key

[shanedeeodonnell]

@Connoropolous sweet thanks! Might as well cache the node_modues while we're at it. Makes sense to me.