feat(gs/system): Setup sccache for rust

Change-Id: Id102a25013d6a99f3db4f082a9feee87eadcd523
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2250
Tested-by: BuildkiteCI
Reviewed-by: glittershark <grfn@gws.fyi>

users/glittershark/system/home/modules/development/rust.nix

@@ -6,6 +6,8 @@
     rustup
     rust-analyzer
     cargo-edit
+    cargo-expand
+    sccache
   ];
 
   programs.zsh.shellAliases = {
@@ -13,4 +15,9 @@
     "cb" = "cargo build";
     "ct" = "cargo test";
   };
+
+  home.file.".cargo/config".text = ''
+    [build]
+    rustc-wrapper = "${pkgs.sccache}/bin/sccache"
+  '';
 }