LRU cache over grpc

Dependencies

• https://github.com/bufbuild/buf needed for generating protobufs with make proto (buf generate)

TODO

• Update volume sharing to be more specific so we're not sharing all of $HOME
  • Maybe to ~/.grpc-lru-cache dir, but would that then need to be initialized in some way? Come back to this.
• Update save to disk to save the items in the correct order