feat(tvix/store): build rust proto files

This uses prost-build to build the proto files.

Change-Id: Ia99fcfa4a19c741683cf28a45202e1d9211f9131
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7286
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>
Reviewed-by: Adam Joseph <adam@westernsemico.com>

tvix/shell.nix

@@ -6,10 +6,12 @@
 pkgs.mkShell {
   name = "tvix-eval-dev-env";
   packages = [
+    pkgs.buf-language-server
     pkgs.cargo
     pkgs.clippy
     pkgs.rust-analyzer
     pkgs.rustc
     pkgs.rustfmt
+    pkgs.protobuf
   ];
 }