Move zstd to emacs module

nix/modules/emacs.nix

@@ -7,6 +7,8 @@
   home.packages = with pkgs; [
     # Needed on macOS because Emacs wants the GNU version of some utilities like ls
     coreutils
+    # Required by nativeComp but not a dependency for some reason
+    zstd
     nodePackages.pyright
   ];
 }